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Currently, the following ciphers are accessible:. In case the user space header files do not export these flags yet, use the following macros:. A cipher is accessed with the same name as done for the in-kernel API calls. This includes the generic vs. To interact with the kernel crypto API, a socket must be created by the user space application. The following API calls assume that the socket descriptor is already opened by the user space application and discusses only the kernel crypto API specific invocations.
Just like the in-kernel operation of the kernel crypto API, the user space interface allows the cipher operation in-place. This is of particular interest for symmetric cipher operations where a copying of the output data to its final destination can be avoided.
If a consumer on the other hand wants to maintain the plaintext and the ciphertext in different memory locations, all a consumer needs to do is to provide different memory pointers for the encryption and decryption operation. The message digest type to be used for the cipher operation is selected when invoking the bind syscall. This data structure must be filled as follows:.
Please see below for the setsockopt interface that explains how the key can be set for a keyed message digest. Using the send system call, the application provides the data that should be processed with the message digest. The send system call allows the following flags to be specified:. With the recv system call, the application can read the message digest from the kernel crypto API.
The operation is very similar to the message digest discussion. During initialization, the struct sockaddr data structure must be filled as follows:. The key setting is described with the setsockopt invocation below. Using the sendmsg system call, the application provides the data that should be processed for encryption or decryption. In addition, the IV is specified with the data structure provided by the sendmsg system call.
The sendmsg system call parameter of struct msghdr is embedded into the struct cmsghdr data structure. That cmsghdr data structure holds the following information specified with a separate header instances:. With the recv system call, the application can read the result of the cipher operation from the kernel crypto API. The output buffer must be at least as large as to hold all blocks of the encrypted or decrypted data. If the output data size is smaller, only as many blocks are returned that fit into that output buffer size.
The operation is very similar to the symmetric cipher discussion. To set the authentication tag size, the caller must use the setsockopt invocation described below. The output buffer must be at least as large as defined with the memory structure below. If the output data size is smaller, the cipher operation is not performed. The authenticated decryption operation may indicate an integrity error. The AEAD cipher operates with the following information that is communicated between user and kernel space as one data stream:.
The sizes of the AAD and the authentication tag are provided with the sendmsg and setsockopt calls see there. As the kernel knows the size of the entire data stream, the kernel is now able to calculate the right offsets of the data components in the data stream.
The output buffer the user space caller provides must be at least as large to hold the following data:. Again, the operation is very similar to the other APIs. The seed is provided using the setsockopt interface to set the key. The DRBGs do not require a seed, but may be seeded. The kernel generates at most bytes in one call. In this case, the returned file descriptors have the same state.
As the name indicates, the kernel tries to avoid a copy operation into kernel space. The zero-copy operation requires data to be aligned at the page boundary. Non-aligned data can be used as well, but may require more operations of the kernel which would defeat the speed gains obtained from the zero-copy interface. The system-interent limit for the size of one zero-copy operation is 16 pages. Zero-copy can be used with the following code example a complete working example is provided with libkcapi :.
This additional information is set using the setsockopt system call that must be invoked with the file descriptor of the open cipher i. Please see  for libkcapi which provides an easy-to-use wrapper around the aforementioned Netlink kernel interface.
This API is obsolete and will be removed in the future. Different IV generators are available. Any variable not documented here shall not be used by a cipher implementation as it is internal to the Crypto API. All fields except givencrypt , givdecrypt , geniv and ivsize are mandatory and must be filled. All fields except geniv and ivsize are mandatory and must be filled.
Asynchronous cipher operations imply that the function invocation for a cipher request returns immediately before the completion of the operation. The cipher request is scheduled as a separate kernel thread and therefore load-balanced on the different CPUs via the process scheduler. To allow the kernel crypto API to inform the caller about the completion of a cipher request, the caller must provide a callback function.
That function is invoked with the cipher handle when the request completes. To support the asynchronous operation, additional information than just the cipher handle must be supplied to the kernel crypto API. For the symmetric key cipher API, the state is maintained with the tfm cipher handle. A single tfm can be used across multiple calls and in parallel. For asynchronous block cipher calls, context data supplied and only used by the caller can be referenced the request data structure in addition to the IV used for the cipher request.
The maintenance of such state information would be important for a crypto driver implementer to have, because when calling the callback function upon completion of the cipher operation, that callback function may need some information about which operation just finished if it invoked multiple in parallel. This state information is unused by the kernel crypto API. Allocate a cipher handle for an skcipher. The size of the IV for the skcipher referenced by the cipher handle is returned.
This IV size may be zero if the cipher does not need an IV. The block size for the skcipher referenced with the cipher handle is returned. The caller may use that information to allocate appropriate memory for the data returned by the encryption or decryption operation. Note, the key length determines the cipher type. Allow the caller to replace the existing skcipher handle in the request data structure with a different one.
Allocate the request data structure that must be used with the skcipher encrypt and decrypt API calls. During the allocation, the provided skcipher handle is registered in the request data structure. This function allows setting the callback function that is triggered once the cipher operation completes. For encryption, the source is treated as the plaintext and the destination is the ciphertext.
For a decryption operation, the use is reversed - the source is the ciphertext and the destination is the plaintext. For the asynchronous block cipher API, the state is maintained with the tfm cipher handle. Allocate a cipher handle for an ablkcipher. The size of the IV for the ablkcipher referenced by the cipher handle is returned.
The block size for the ablkcipher referenced with the cipher handle is returned. Allow the caller to replace the existing ablkcipher handle in the request data structure with a different one. Allocate the request data structure that must be used with the ablkcipher encrypt and decrypt API calls. During the allocation, the provided ablkcipher handle is registered in the request data structure. However, the kernel supports other types of AEAD ciphers which are defined with the following cipher string:.
The example code provided for the symmetric key cipher operation applies here as well. Naturally all skcipher symbols must be exchanged the aead pendants discussed in the following. In case of an encryption, the associated data memory is filled during the encryption operation. For decryption, the associated data memory must contain data that is used to verify the integrity of the decrypted data.
That error indicates an authentication error, i. It is important to note that if multiple scatter gather list entries form the input data mentioned above, the first entry must not point to a NULL buffer. If there is any potential where the AAD buffer can be NULL, the calling code must contain a precaution to ensure that this does not result in the first scatter gather list entry pointing to a NULL buffer. Allocate a cipher handle for an AEAD.
The size of the IV for the aead referenced by the cipher handle is returned. The authentication data size may be zero if the cipher implements a hard-coded maximum. The block size for the AEAD referenced with the cipher handle is returned. Allow the caller to replace the existing aead handle in the request data structure with a different one.
During the allocation, the provided aead handle is registered in the request data structure. See below for the authentication tag. The content of the AD in the destination buffer after processing will either be untouched, or it will contain a copy of the AD from the source buffer. In order to ensure that it always has a copy of the AD, the user must copy the AD over either before or after processing. Synchronous calls, have a context in the tfm. But since a single tfm can be used in multiple calls and in parallel, this info should not be changeable unless a lock is used.
This applies, for example, to the symmetric key. So, its the only state info that can be kept for synchronous calls without using a big lock across a tfm. The block cipher API allows the use of a complete cipher, i.
After the completion of the cipher operation, the plaintext data is replaced with the ciphertext data in case of an encryption and vice versa for a decryption. Allocate a cipher handle for a block cipher. The size of the IV for the block cipher referenced by the cipher handle is returned. The block size for the block cipher referenced with the cipher handle is returned. The caller must fill desc as follows: desc.
Encrypt plaintext data with the use of an IV that is solely used for this cipher operation. Any previously set IV is not used. Decrypt ciphertext data with the use of an IV that is solely used for this cipher operation. The caller can obtain the IV set for the block cipher referenced by the cipher handle and store it into the user-provided buffer. If the buffer has an insufficient space, the IV is truncated to fit the buffer.
Using the single block cipher API calls, operations with the basic cipher primitive can be implemented. These cipher primitives exclude any block chaining operations including IV handling. The purpose of this single block cipher API is to support the implementation of templates or other concepts that only need to perform the cipher operation on one block at a time. Templates invoke the underlying cipher primitive block-wise and process either the input or the output data of these cipher operations.
Allocate a cipher handle for a single block cipher. The block size for the single block cipher referenced with the cipher handle tfm is returned. Invoke the encryption operation of one block. The caller must ensure that the plaintext and ciphertext buffers are at least one block in size.
Invoke the decryption operation of one block. Allocate a cipher handle for an ahash. Any potentially existing state created by previous operations is discarded. The size for the message digest created by the message digest cipher referenced with the cipher handle is returned. Return the size of the ahash state size. The caller provided key is set for the ahash cipher.
The cipher handle must point to a keyed hash in order for this function to succeed. The parameters have the same meaning as discussed for those separate functions. Finalize the message digest operation and create the message digest based on all data added to the cipher handle. The parameters have the same meaning as discussed for those separate three functions. Allow the caller to replace the existing ahash handle in the request data structure with a different one.
Allocate the request data structure that must be used with the ahash message digest API calls. During the allocation, the provided ahash handle is registered in the request data structure. Allocate a cipher handle for a message digest. The size of the operational state the cipher needs during operation is returned for the hash referenced with the cipher handle. This size is required to calculate the memory requirements to allow the caller allocating sufficient memory for operational state.
The caller provided key is set for the keyed message digest cipher. The cipher handle must point to a keyed message digest cipher in order for this function to succeed. This function exports the hash state of the operational state handle into the caller-allocated output buffer out which must have sufficient size e. After the conversation we had a deal. I've paid the price after agreement about the possibility of the payment, but they wrote that they was changed the idea and I need to pay the same price one more time.
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I understand. Void Tags. Industry Gaming. Void to USD Chart. Here are some other articles that you may be interested in: What Is a Crypto Faucet? What Are Crypto Debit Cards? Cryptanalysts trying to break the ciphertext will have an easier job if they note blocks of repeating text.
In order to add more complexity to the text, feedback modes use the previous block of output to alter the input blocks before applying the encryption algorithm. The first block will need an initial value, and this value is called the initialization vector IV. Since the IV simply alters the data before any encryption, the IV should be random but does not necessarily need to be kept secret. ECB Electronic Codebook Mode is a mode in which there is no influence from block position or other ciphertext blocks.
Encryption using a longer key generally implies a stronger resistance to message recovery. As usual, there is a trade off between security and time, so choose the key length appropriately. Most algorithms use binary keys. Most humans do not have the ability to remember long sequences of binary numbers, even when represented in hexadecimal. Character passwords are much easier to recall. Because character passwords are generally chosen from a small number of characters for example, [a-zA-Z] , protocols such as "Password-Based Encryption" PBE have been defined which take character passwords and generate strong binary keys.
For example, some data might not need to be kept confidential, but should figure into the tag calculation to detect modifications. The Cipher. If just a transformation name is specified, the system will determine if there is an implementation of the requested transformation available in the environment, and if there is more than one, returns there is a preferred one. If both a transformation name and a package provider are specified, the system will determine if there is an implementation of the requested transformation in the package requested, and throw an exception if there is not.
It is recommended to use a transformation that fully specifies the algorithm, mode, and padding. By not doing so, the provider will use a default. ECB works well for single blocks of data, but absolutely should not be used for multiple data blocks.
If no such number is specified, a provider-specific default is used. Appendix A of this document contains a list of standard names that can be used to specify the algorithm name, mode, and padding scheme components of a transformation. The objects returned by factory methods are uninitialized, and must be initialized before they become usable.
A Cipher object obtained via getInstance must be initialized for one of four modes, which are defined as final integer constants in the Cipher class. The modes can be referenced by their symbolic names, which are shown below along with a description of the purpose of each mode:. Each of the Cipher initialization methods takes an operational mode parameter opmode , and initializes the Cipher object for that mode.
Other parameters include the key key or certificate containing the key certificate , algorithm parameters params , and a source of randomness random. If a Cipher object that requires parameters e. However, if a Cipher object that requires parameters is initialized for decryption, and no parameters are supplied to the init method, an InvalidKeyException or InvalidAlgorithmParameterException exception will be raised, depending on the init method that has been used.
See the section about Managing Algorithm Parameters for more details. Note that when a Cipher object is initialized, it loses all previously-acquired state. In other words, initializing a Cipher is equivalent to creating a new instance of that Cipher, and initializing it. For example, if a Cipher is first initialized for decryption with a given key, and then initialized for encryption, it will lose any state acquired while in decryption mode. Data can be encrypted or decrypted in one step single-part operation or in multiple steps multiple-part operation.
A multiple-part operation is useful if you do not know in advance how long the data is going to be, or if the data is too long to be stored in memory all at once. A multiple-part operation must be terminated by one of the above doFinal methods if there is still some input data left for the last step , or by one of the following doFinal methods if there is no input data left for the last step :.
All the doFinal methods take care of any necessary padding or unpadding , if padding or unpadding has been requested as part of the specified transformation. A call to doFinal resets the Cipher object to the state it was in when initialized via a call to init. That is, the Cipher object is reset and available to encrypt or decrypt depending on the operation mode that was specified in the call to init more data. These methods also enable the possibility of secure transfer of hardware-based keys.
If you are supplying the wrapped key bytes the result of calling wrap to someone else who will unwrap them, be sure to also send additional information the recipient will need in order to do the unwrap :.
The key algorithm name can be determined by calling the getAlgorithm method from the Key interface:. Here, wrappedKey is the bytes returned from the previous call to wrap, wrappedKeyAlgorithm is the algorithm associated with the wrapped key, and wrappedKeyType is the type of the wrapped key.
This must be one of Cipher. The parameters being used by the underlying Cipher implementation, which were either explicitly passed to the init method by the application or generated by the underlying implementation itself, can be retrieved from the Cipher object by calling its getParameters method, which returns the parameters as a java.
AlgorithmParameters object or null if no parameters are being used. If the parameter is an initialization vector IV , it can also be retrieved by calling the getIV method. In the following example, a Cipher object implementing password-based encryption PBE is initialized with just a key and no parameters.
However, the selected algorithm for password-based encryption requires two parameters - a salt and an iteration count. Those will be generated by the underlying algorithm implementation itself. The application can retrieve the generated parameters from the Cipher object as follows:. The same parameters that were used for encryption must be used for decryption. They can be instantiated from their encoding and used to initialize the corresponding Cipher object for decryption, as follows:.
If you did not specify any parameters when you initialized a Cipher object, and you are not sure whether or not the underlying implementation uses any parameters, you can find out by simply calling the getParameters method of your Cipher object and checking the value returned.
A return value of null indicates that no parameters were used. Note that you do not have to worry about storing or transferring any algorithm parameters for use by the decryption operation if you use the SealedObject class.
This class attaches the parameters used for sealing encryption to the encrypted object contents, and uses the same parameters for unsealing decryption. Some of the update and doFinal methods of Cipher allow the caller to specify the output buffer into which to encrypt or decrypt the data. In these cases, it is important to pass a buffer that is large enough to hold the result of the encryption or decryption operation.
This class is a FilterInputStream that encrypts or decrypts the data passing through it. It is composed of an InputStream , or one of its subclasses, and a Cipher. CipherInputStream represents a secure input stream into which a Cipher object has been interposed. The read methods of CipherInputStream return data that are read from the underlying InputStream but have additionally been processed by the embedded Cipher object.
The Cipher object must be fully initialized before being used by a CipherInputStream. For example, if the embedded Cipher has been initialized for decryption, the CipherInputStream will attempt to decrypt the data it reads from the underlying InputStream before returning them to the application.
This class adheres strictly to the semantics, especially the failure semantics, of its ancestor classes java. FilterInputStream and java. This class has exactly those methods specified in its ancestor classes, and overrides them all, so that the data are additionally processed by the embedded cipher. Moreover, this class catches all exceptions that are not thrown by its ancestor classes.
In particular, the skip long method skips only data that has been processed by the Cipher. It is crucial for a programmer using this class not to use methods that are not defined or overridden in this class such as a new method or constructor that is later added to one of the super classes , because the design and implementation of those methods are unlikely to have considered security impact with regard to CipherInputStream. As an example of its usage, suppose cipher1 has been initialized for encryption.
The code below demonstrates how to use a CipherInputStream containing that cipher and a FileInputStream in order to encrypt input stream data:. In this example, assume that cipher1 and cipher2 have been initialized for encryption and decryption with corresponding keys , respectively. Of course since this program simply encrypts text and decrypts it back right away, it's actually not very useful except as a simple way of illustrating chaining of CipherInputStreams. Note that the read methods of the CipherInputStream will block until data is returned from the underlying cipher.
If a block cipher is used, a full block of cipher text will have to be obtained from the underlying InputStream. This class is a FilterOutputStream that encrypts or decrypts the data passing through it. It is composed of an OutputStream , or one of its subclasses, and a Cipher.
CipherOutputStream represents a secure output stream into which a Cipher object has been interposed. The write methods of CipherOutputStream first process the data with the embedded Cipher object before writing them out to the underlying OutputStream. The Cipher object must be fully initialized before being used by a CipherOutputStream. For example, if the embedded Cipher has been initialized for encryption, the CipherOutputStream will encrypt its data, before writing them out to the underlying output stream.
OutputStream and java. This class has exactly those methods specified in its ancestor classes, and overrides them all, so that all data are additionally processed by the embedded cipher. It is crucial for a programmer using this class not to use methods that are not defined or overridden in this class such as a new method or constructor that is later added to one of the super classes , because the design and implementation of those methods are unlikely to have considered security impact with regard to CipherOutputStream.
The code below demonstrates how to use a CipherOutputStream containing that cipher and a FileOutputStream in order to encrypt data to be written to an output stream:. The following example demonstrates how to easily connect several instances of CipherOutputStream and FileOutputStream. In this example, assume that cipher1 and cipher2 have been initialized for decryption and encryption with corresponding keys , respectively:. One thing to keep in mind when using block cipher algorithms is that a full block of plaintext data must be given to the CipherOutputStream before the data will be encrypted and sent to the underlying output stream.
There is one other important difference between the flush and close methods of this class, which becomes even more relevant if the encapsulated Cipher object implements a block cipher algorithm with padding turned on:. This class enables a programmer to create an object and protect its confidentiality with a cryptographic algorithm. Given any object that implements the java. Serializable interface, one can create a SealedObject that encapsulates the original object, in serialized format i.
The encrypted content can later be decrypted with the corresponding algorithm using the correct decryption key and deserialized, yielding the original object. A typical usage is illustrated in the following code segment: In order to seal an object, you create a SealedObject from the object to be sealed and a fully initialized Cipher object that will encrypt the serialized object contents.
Note that any algorithm parameters that may be used in the sealing operation are stored inside of SealedObject :. This approach has the advantage that the party who unseals the sealed object does not require knowledge of the decryption key. For example, after one party has initialized the cipher object with the required decryption key, it could hand over the cipher object to another party who then unseals the sealed object.
In this approach, the getObject method creates a cipher object for the appropriate decryption algorithm and initializes it with the given decryption key and the algorithm parameters if any that were stored in the sealed object. This approach has the advantage that the party who unseals the object does not need to keep track of the parameters e.
Similar to a MessageDigest , a Message Authentication Code MAC provides a way to check the integrity of information transmitted over or stored in an unreliable medium, but includes a secret key in the calculation. Only someone with the proper key will be able to verify the received message.
Typically, message authentication codes are used between two parties that share a secret key in order to validate information transmitted between these parties. HMAC can be used with any cryptographic hash function, e. Please refer to the code example. A Mac object is always initialized with a secret key and may optionally be initialized with a set of parameters, depending on the underlying MAC algorithm. You can initialize your Mac object with any secret- key object that implements the javax.
SecretKey interface. This could be an object returned by javax. With others, however, the secret- key algorithm does matter, and an InvalidKeyException is thrown if a secret- key object with an inappropriate secret- key algorithm is used. A MAC can be computed in one step single-part operation or in multiple steps multiple-part operation.
To compute the MAC of some data in a single step, call the following doFinal method:. A multiple-part operation must be terminated by the above doFinal method if there is still some input data left for the last step , or by one of the following doFinal methods if there is no input data left for the last step :. It is now time to turn our attention to keys.
The java. Key interface is the top-level interface for all opaque keys. It defines the functionality shared by all opaque key objects. An opaque key representation is one in which you have no direct access to the key material that constitutes a key. In other words: "opaque" gives you limited access to the key--just the three methods defined by the Key interface see below : getAlgorithm , getFormat , and getEncoded. This is in contrast to a transparent representation, in which you can access each key material value individually, through one of the get methods defined in the corresponding specification class.
It is also possible to parse certificates, using a CertificateFactory. Here is a list of interfaces which extend the Key interface in the java. The PublicKey and PrivateKey interfaces which both extend the Key interface are methodless interfaces, used for type-safety and type-identification.
The KeyPair class is a simple holder for a key pair a public key and a private key. It has two public methods, one for returning the private key, and the other for returning the public key:. Key objects and key specifications KeySpec s are two different representations of key data. Cipher s use Key objects to initialize their encryption algorithms, but keys may need to be converted into a more portable format for transmission or storage.
A transparent representation of keys means that you can access each key material value individually, through one of the get methods defined in the corresponding specification class. If the key is stored on a hardware device, its specification may contain information that helps identify the key on the device. This representation is contrasted with an opaque representation, as defined by the Key interface, in which you have no direct access to the key material fields.
In other words, an "opaque" representation gives you limited access to the key--just the three methods defined by the Key interface: getAlgorithm , getFormat , and getEncoded. A key may be specified in an algorithm-specific way, or in an algorithm-independent encoding format such as ASN.
The KeyFactory and SecretKeyFactory classes can be used to convert between opaque and transparent key representations that is, between Key s and KeySpec s, assuming that the operation is possible. For example, private keys on smart cards might not be able leave the card.
Such Key s are not convertible. In the following sections, we discuss the key specification interfaces and classes in the java. This interface contains no methods or constants. Its only purpose is to group and provide type safety for all key specifications.
All key specifications must implement this interface. Generators are used to generate brand new objects. Generators can be initialized in either an algorithm-dependent or algorithm-independent way. For example, to create a Diffie-Hellman DH keypair, an application could specify the necessary P and G values, or the generator could simply be initialized with the appropriate key length, and the generator will select appropriate P and G values.
In both cases, the generator will produce brand new keys based on the parameters. On the other hand, factories are used to convert data from one existing object type to another. For example, an application might have available the components of a DH private key and can package them as a KeySpec , but needs to convert them into a PrivateKey object that can be used by a KeyAgreement object, or vice-versa. Or they might have the byte array of a certificate, but need to use a CertificateFactory to convert it into a XCertificate object.
Applications use factory objects to do the conversion. The KeyFactory class is an engine class designed to perform conversions between opaque cryptographic Key s and key specifications transparent representations of the underlying key material. Key factories are bidirectional. They allow you to build an opaque key object from a given key specification key material , or to retrieve the underlying key material of a key object in a suitable format.
Multiple compatible key specifications can exist for the same key. For example, a DSA public key may be specified by its components y , p , q , and g see java. A key factory can be used to translate between compatible key specifications. Key parsing can be achieved through translation between compatible key specifications, e.
KeyFactory objects are obtained by using one of the KeyFactory getInstance static factory methods. If you have a key specification for a public key, you can obtain an opaque PublicKey object from the specification by using the generatePublic method:. Similarly, if you have a key specification for a private key, you can obtain an opaque PrivateKey object from the specification by using the generatePrivate method:.
If you have a Key object, you can get a corresponding key specification object by calling the getKeySpec method:. This class represents a factory for secret keys. Unlike KeyFactory , a javax. SecretKeyFactory object operates only on secret symmetric keys, whereas a java.
KeyFactory object processes the public and private key components of a key pair. Key factories are used to convert Key s opaque cryptographic keys of type java. Key into key specifications transparent representations of the underlying key material in a suitable format , and vice versa.
Objects of type java. Key , of which java. PublicKey , java. PrivateKey , and javax. SecretKey are subclasses, are opaque key objects, because you cannot tell how they are implemented. The underlying implementation is provider-dependent, and may be software or hardware based. Key factories allow providers to supply their own implementations of cryptographic keys. For example, if you have a key specification for a Diffie Hellman public key, consisting of the public value y , the prime modulus p , and the base g , and you feed the same specification to Diffie-Hellman key factories from different providers, the resulting PublicKey objects will most likely have different underlying implementations.
A provider should document the key specifications supported by its secret key factory. The following is an example of how to use a SecretKeyFactory to convert secret key data into a SecretKey object, which can be used for a subsequent Cipher operation:.
In this case, the underlying implementation of SecretKey is based on the provider of KeyFactory. An alternative, provider-independent way of creating a functionally equivalent SecretKey object from the same key material is to use the javax. SecretKeySpec class, which implements the javax. SecretKey interface:. If you have a key specification for a secret key, you can obtain an opaque SecretKey object from the specification by using the generateSecret method:.
If you have a Secret Key object, you can get a corresponding key specification object by calling the getKeySpec method:. The KeyPairGenerator class is an engine class used to generate pairs of public and private keys. There are two ways to generate a key pair: in an algorithm-independent manner, and in an algorithm-specific manner.
The only difference between the two is the initialization of the object. Please see the Examples section for examples of calls to the methods documented below. All key pair generation starts with a KeyPairGenerator. A key pair generator needs to be initialized before it can generate keys. In most cases, algorithm-independent initialization is sufficient. But in other cases, algorithm-specific initialization can be used. All key pair generators share the concepts of a keysize and a source of randomness.
The keysize is interpreted differently for different algorithms. For example, in the case of the DSA algorithm, the keysize corresponds to the length of the modulus. See the Standard Names document for information about the keysizes for specific algorithms. Since no other parameters are specified when you call the above algorithm-independent initialize methods, it is up to the provider what to do about the algorithm-specific parameters if any to be associated with each of the keys.
If the algorithm is a "DSA" algorithm, and the modulus size keysize is , , or , then the SUN provider uses a set of precomputed values for the p , q , and g parameters. If the modulus size is not one of the above values, the SUN provider creates a new set of parameters.
Other providers might have precomputed parameter sets for more than just the three modulus sizes mentioned above. Still others might not have a list of precomputed parameters at all and instead always create new parameter sets. For situations where a set of algorithm-specific parameters already exists such as "community parameters" in DSA , there are two initialize methods that have an AlgorithmParameterSpec argument.
One also has a SecureRandom argument, while the source of randomness is system-provided for the other:. The procedure for generating a key pair is always the same, regardless of initialization and of the algorithm. You always call the following method from KeyPairGenerator :. A key generator for a particular symmetric-key algorithm creates a symmetric key that can be used with that algorithm.
It also associates algorithm-specific parameters if any with the generated key. There are two ways to generate a key: in an algorithm-independent manner, and in an algorithm-specific manner. The only difference between the two is the initialization of the object:. All key generators share the concepts of a keysize and a source of randomness. There is an init method that takes these two universally shared types of arguments.
There is also one that takes just a keysize argument, and uses a system-provided source of randomness, and one that takes just a source of randomness:. Since no other parameters are specified when you call the above algorithm-independent init methods, it is up to the provider what to do about the algorithm-specific parameters if any to be associated with the generated key. For situations where a set of algorithm-specific parameters already exists, there are two init methods that have an AlgorithmParameterSpec argument.
In case the client does not explicitly initialize the KeyGenerator via a call to an init method , each provider must supply and document a default initialization. Key agreement is a protocol by which 2 or more parties can establish the same cryptographic keys, without having to exchange any secret information.
Each party initializes their key agreement object with their private key, and then enters the public keys for each party that will participate in the communication. In most cases, there are just two parties, but algorithms such as Diffie-Hellman allow for multiple parties 3 or more to participate. When all the public keys have been entered, each KeyAgreement object will generate agree upon the same key. The KeyAgreement class provides the functionality of a key agreement protocol. The keys involved in establishing a shared secret are created by one of the key generators KeyPairGenerator or KeyGenerator , a KeyFactory , or as a result from an intermediate phase of the key agreement protocol.
Each party involved in the key agreement has to create a KeyAgreement object. KeyAgreement objects are obtained by using one of the KeyAgreement getInstance static factory methods. You initialize a KeyAgreement object with your private information. In the case of Diffie-Hellman, you initialize it with your Diffie-Hellman private key. Note that if the requested key agreement algorithm requires the specification of algorithm parameters, and only a key, but no parameters are provided to initialize the KeyAgreement object, the key must contain the required algorithm parameters.
For example, the Diffie-Hellman algorithm uses a prime modulus p and a base generator g as its parameters. Every key agreement protocol consists of a number of phases that need to be executed by each party involved in the key agreement. The key parameter contains the key to be processed by that phase. In most cases, this is the public key of one of the other parties involved in the key agreement, or an intermediate key that was generated by a previous phase. The lastPhase parameter specifies whether or not the phase to be executed is the last one in the key agreement: A value of FALSE indicates that this is not the last phase of the key agreement there are more phases to follow , and a value of TRUE indicates that this is the last phase of the key agreement and the key agreement is completed, i.
After each party has executed all the required key agreement phases, it can compute the shared secret by calling one of the generateSecret methods:. The user keystore is by default stored in a file named. On Solaris systems "user. On Win32 systems, given user name uName , "user. In addition to the user's keystore, the JDK also maintains a system-wide keystore which is used to store trusted certificates from a variety of Certificate Authorities CA's.
These CA certificates can be used to help make trust decisions. Instead of using the system-wide cacerts keystore, applications can set up and use their own keystores, or even use the user keystore described above. Currently, there are two command-line tools that make use of KeyStore : keytool and jarsigner , and also a GUI-based tool named policytool. It is also used by the Policy reference implementation when it processes policy files specifying the permissions allowed accesses to system resources to be granted to code from various sources.
Since KeyStore is publicly available, JDK users can write additional security applications that use it. Applications can choose different types of keystore implementations from different providers, using the getInstance factory method in the KeyStore class. A keystore type defines the storage and data format of the keystore information, and the algorithms used to protect private keys in the keystore and the integrity of the keystore itself.
Keystore implementations of different types are not compatible. The recommended keystore implementation is "pkcs12". This standard is primarily meant for storing or transporting a user's private keys, certificates, and miscellaneous secrets. Arbitrary attributes can be associated with individual entries in a PKCS12 keystore. The default keystore implementation type is "jks", which is specified in the following line in the java. To have tools and other applications use a different default keystore implementation, you can change that line to specify another default type.
For example, to use "pkcs12" as the default keystore implementation, change the line to:. Some applications, such as keytool , also let you override the default keystore type via the -storetype command-line parameter. The "jceks" implementation can parse and convert a "jks" keystore file to the "jceks" format. You may upgrade your keystore of type "jks" to a keystore of type "jceks" by changing the password of a private-key entry in your keystore and specifying -storetype jceks as the keystore type.
To apply the cryptographically strong er key protection supplied to a private key named "signkey" in your default keystore, use the following command, which will prompt you for the old and new key passwords:. See Security Tools for more information about keytool and about keystores and how they are managed. Keystore implementations are provider-based. Developers interested in writing their own KeyStore implementations should consult How to Implement a Provider for the Java Cryptography Architecture for more information on this topic.
The KeyStore class is an engine class that supplies well-defined interfaces to access and modify the information in a keystore. This class represents an in-memory collection of keys and certificates. KeyStore manages two types of entries:. This type of keystore entry holds very sensitive cryptographic key information, which is stored in a protected format to prevent unauthorized access. Typically, a key stored in this type of entry is a secret key, or a private key accompanied by the certificate chain authenticating the corresponding public key.
Private keys and certificate chains are used by a given entity for self-authentication using digital signatures. This type of entry contains a single public key certificate belonging to another party. It is called a trusted certificate because the keystore owner trusts that the public key in the certificate indeed belongs to the identity identified by the subject owner of the certificate.
Whether keystores are persistent, and the mechanisms used by the keystore if it is persistent, are not specified here. This convention allows use of a variety of techniques for protecting sensitive e. Smart cards or other integrated cryptographic engines SafeKeyper are one option, and simpler mechanisms such as files may also be used in a variety of formats. KeyStore objects are obtained by using one of the KeyStore getInstance static factory methods.
To create an empty keystore, you pass null as the InputStream argument to the load method. All keystore entries are accessed via unique aliases. The aliases method returns an enumeration of the alias names in the keystore:. The setKeyEntry methods add if alias doesn't yet exist or set key entries:.
A transparent representation of a set of parameters via AlgorithmParameterSpec means that you can access each parameter value in the set individually. You can access these values through one of the get methods defined in the corresponding specification class e.
In contrast, the AlgorithmParameters class supplies an opaque representation, in which you have no direct access to the parameter fields. You can only get the name of the algorithm associated with the parameter set via getAlgorithm and some kind of encoding for the parameter set via getEncoded.
The algorithm parameter specification interfaces and classes in the java. The following algorithm parameter specs are used specifically for digital signatures, as part of JSR AlgorithmParameters objects are obtained by using one of the AlgorithmParameters getInstance static factory methods. Once an AlgorithmParameters object is instantiated, it must be initialized via a call to init , using an appropriate parameter specification or parameter encoding:.
A byte encoding of the parameters represented in an AlgorithmParameters object may be obtained via a call to getEncoded :. A transparent parameter specification for the algorithm parameters may be obtained from an AlgorithmParameters object via a call to getParameterSpec :.
AlgorithmParameterGenerator objects are obtained by using one of the AlgorithmParameterGenerator getInstance static factory methods. The AlgorithmParameterGenerator object can be initialized in two different ways: an algorithm-independent manner or an algorithm-specific manner. The algorithm-independent approach uses the fact that all parameter generators share the concept of a "size" and a source of randomness.
The measure of size is universally shared by all algorithm parameters, though it is interpreted differently for different algorithms. For example, in the case of parameters for the DSA algorithm, "size" corresponds to the size of the prime modulus, in bits. See the Standard Names document for information about the sizes for specific algorithms.
When using this approach, algorithm-specific parameter generation values--if any--default to some standard values. One init method that takes these two universally shared types of arguments:. A third approach initializes a parameter generator object using algorithm-specific semantics, which are represented by a set of algorithm-specific parameter generation values supplied in an AlgorithmParameterSpec object:.
A certificate factory for X. XCertificate , and CRLs that are an instance of java. CertificateFactory objects are obtained by using one of the getInstance static factory methods. To generate a CertPath object and initialize it with data read from an input stream, use one of the following generateCertPath methods with or without specifying the encoding to be used for the data :. A concrete implementation of the Provider class is first written that will eventually be registered in the Security class' list of providers.
This provider mainly provides a mapping from algorithm names to actual implementation classes. Before discussing details of the actual handshake, a quick review of some of the JSSE's architecture is needed. SSLContext s are initialized with two callback classes, KeyManager and TrustManager , which allow applications to first select authentication material to send and second to verify credentials sent by a peer.
When a KeyStore object is initialized and loaded from the file, the file's raw bytes are converted into PublicKey and PrivateKey objects using a KeyFactory , and a certificate chain's bytes are converted using a CertificateFactory. When a credential is needed, the KeyManager simply consults this KeyStore object and determines which credentials to present. A KeyStore 's contents might have originally been created using a utility such as keytool.
This generator is then used to create a KeyPair which keytool would store along with the newly-created certificate in the KeyStore , which is eventually written to disk. Internally, the CertPath implementation might create a Signature object, and use that to verify that the each of the signatures in the certificate chain.
The client begins by sending a ClientHello message to the server. The server selects a ciphersuite to use, and sends that back in a ServerHello message, and begins creating JCA objects based on the suite selection. We'll use server-only authentication in the following examples. The client's TrustManager verifies the server's certificate, and if accepted, the client generates some random bytes using a SecureRandom object.
This is then encrypted using an encrypting asymmetric RSA Cipher object that has been initialized with the PublicKey found in the server's certificate. This encrypted data is sent in a Client Key Exchange message. The server would use its corresponding PrivateKey to recover the bytes using a similar Cipher in decrypt mode. These bytes are then used to establish the actual encryption keys. The server sends its public key pieces in a ServerKeyExchange message protected by the DSA signature algorithm, and the client sends its public key in a ClientKeyExchange message.
When the public keys are reassembled using another KeyFactory , they are fed into the agreement objects. The KeyAgreement objects then generate agreed-upon bytes that are then used to establish the actual encryption keys. Once the actual encryption keys have been established, the secret key is used to initialize a symmetric Cipher object, and this cipher is used to protect all data in transit. To help determine if the data has been modified, a MessageDigest is created and receives a copy of the data destined for the network.
When the packet is complete, the digest hash is appended to data, and the entire packet is encrypted by the Cipher. If a block cipher such as AES is used, the data must be padded to make a complete block. On the remote side, the steps are simply reversed. Again, this is vastly simplified, but gives one an idea of how these classes might be combined to create a higher level protocol. Note : This section should be ignored by most application developers.
It is only for people whose applications may be exported to those few countries whose governments mandate cryptographic restrictions, if it is desired that such applications have fewer cryptographic restrictions than those mandated. By default, an application can use cryptographic algorithms of any strength.
However, due to import control restrictions by the governments of a few countries, you may have to limit those algorithms' strength. The JCA framework includes an ability to enforce restrictions regarding the maximum strengths of cryptographic algorithms available to applications in different jurisdiction contexts locations.
You specify these restrictions in jurisdiction policy files. It is possible that the governments of some or all such countries may allow certain applications to become exempt from some or all cryptographic restrictions. For example, they may consider certain types of applications as "special" and thus exempt. Or they may exempt any application that utilizes an "exemption mechanism," such as key recovery.
Applications deemed to be exempt could get access to stronger cryptography than that allowed for non-exempt applications in such countries. For an application to be recognized as "exempt" at runtime, it must meet the following conditions:. Below are sample steps required in order to make an application exempt from some cryptographic restrictions. This is a basic outline that includes information about what is required by JCA in order to recognize and treat applications as being exempt.
You will need to know the exemption requirements of the particular country or countries in which you would like your application to be able to be run but whose governments require cryptographic restrictions.
You will also need to know the requirements of a JCA framework vendor that has a process in place for handling exempt applications. Consult such a vendor for further information. When an application has a permission policy file associated with it in the same JAR file and that permission policy file specifies an exemption mechanism, then when the Cipher getInstance method is called to instantiate a Cipher , the JCA code searches the installed providers for one that implements the specified exemption mechanism.
If it finds such a provider, JCA instantiates an ExemptionMechanism object associated with the provider's implementation, and then associates the ExemptionMechanism object with the Cipher returned by getInstance. After instantiating a Cipher , and prior to initializing it via a call to the Cipher init method , your code must call the following Cipher method:.
This call returns the ExemptionMechanism object associated with the Cipher. You must then initialize the exemption mechanism implementation by calling the following method on the returned ExemptionMechanism :. The argument you supply should be the same as the argument of the same types that you will subsequently supply to a Cipher init method. Once you have initialized the ExemptionMechanism , you can proceed as usual to initialize and use the Cipher.
In order for an application to be recognized at runtime as being "exempt" from some or all cryptographic restrictions, it must have a permission policy file bundled with it in a JAR file. The permission policy file specifies what cryptography-related permissions the application has, and under what conditions if any.
The format of a permission entry in a permission policy file that accompanies an exempt application is the same as the format for a jurisdiction policy file downloaded with the JDK, which is:. See Appendix B for more information about the jurisdiction policy file format.
Some applications may be allowed to be completely unrestricted. Thus, the permission policy file that accompanies such an application usually just needs to contain the following:.
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