CCCryptor(3cc) LOCAL CCCryptor(3cc)
NAME
CCCryptorCreate, CCryptorCreateFromData, CCCryptorRelease,
CCCryptorUpdate, CCCryptorFinal, CCCryptorGetOutputLength,
CCCryptorReset, CCCrypt -- Common Cryptographic Algorithm Interfaces
LIBRARY
These functions are found in libSystem.
SYNOPSIS
#include <CommonCrypto/CommonCryptor.h>
CCCryptorStatus
CCCryptorCreate(CCOperation op, CCAlgorithm alg, CCOptions options,
const void *key, size_t keyLength, const void *iv,
CCCryptorRef *cryptorRef);
CCCryptorStatus
CCCryptorCreateFromData(CCOperation op, CCAlgorithm alg,
CCOptions options, const void *key, size_t keyLength, const void *iv,
const void *data, size_t dataLength, CCCryptorRef *cryptorRef,
size_t *dataUsed);
CCCryptorStatus
CCCryptorRelease(CCCryptorRef cryptorRef);
CCCryptorStatus
CCCryptorUpdate(CCCryptorRef cryptorRef, const void *dataIn,
size_t dataInLength, void *dataOut, size_t dataOutAvailable,
size_t *dataOutMoved);
CCCryptorStatus
CCCryptorFinal(CCCryptorRef cryptorRef, void *dataOut,
size_t dataOutAvailable, size_t *dataOutMoved);
size_t
CCCryptorGetOutputLength(CCCryptorRef cryptorRef, size_t inputLength,
bool final);
CCCryptorStatus
CCCryptorReset(CCCryptorRef cryptorRef, const void *iv);
CCCryptorStatus
CCCrypt(CCOperation op, CCAlgorithm alg, CCOptions options,
const void *key, size_t keyLength, const void *iv,
const void *dataIn, size_t dataInLength, void *dataOut,
size_t dataOutAvailable, size_t *dataOutMoved);
DESCRIPTION
This interface provides access to a number of symmetric encryption algo-
rithms. Symmetric encryption algorithms come in two "flavors" - block
ciphers, and stream ciphers. Block ciphers process data (while both
encrypting and decrypting) in discrete chunks of data called blocks;
stream ciphers operate on arbitrary sized data.
The object declared in this interface, CCCryptor, provides access to both
block ciphers and stream ciphers with the same API; however some options
are available for block ciphers that do not apply to stream ciphers.
The general operation of a CCCryptor is: initialize it with raw key data
and other optional fields with CCCryptorCreate(); process input data via
one or more calls to CCCryptorUpdate(), each of which may result in out-
put data being written to caller-supplied memory; and obtain possible
remaining output data with CCCryptorFinal(). The CCCryptor is disposed of
via CCCryptorRelease(), or it can be reused (with the same key data as
provided to CCCryptorCreate()) by calling CCCryptorReset().
CCCryptors can be dynamically allocated by this module, or their memory
can be allocated by the caller.
One option for block ciphers is padding, as defined in PKCS7; when pad-
ding is enabled, the total amount of data encrypted does not have to be
an even multiple of the block size, and the actual length of plaintext is
calculated during decryption.
Another option for block ciphers is Cipher Block Chaining, known as CBC
mode. When using CBC mode, an Initialization Vector (IV) is provided
along with the key when starting an encrypt or decrypt operation. If CBC
mode is selected and no IV is provided, an IV of all zeroes will be used.
CCCryptor also implements block bufferring, so that individual calls to
CCCryptorUpdate() do not have to provide data whose length is aligned to
the block size. (If padding is disabled, encrypting with block ciphers
does require that the *total* length of data input to CCCryptorUpdate()
call(s) be aligned to the block size.)
A given CCCryptor can only be used by one thread at a time; multiple
threads can use safely different CCCryptors at the same time.
CCCryptorRef objects created with CCCryptorCreate() or
CCCryptorCreateFromData() *may* be disposed of via CCCRyptorRelease() ;
that call is not strictly necessary, but if it's not performed, good
security practice dictates that the caller should zero the memory pro-
vided to create the CCCryptorRef when the caller is finished using the
CCCryptorRef.
CCCryptorUpdate() is used to encrypt or decrypt data. This routine can
be called multiple times. The caller does not need to align input data
lengths to block sizes; input is bufferred as necessary for block
ciphers.
When performing symmetric encryption with block ciphers, and padding is
enabled via kCCOptionPKCS7Padding, the total number of bytes provided by
all the calls to this function when encrypting can be arbitrary (i.e.,
the total number of bytes does not have to be block aligned). However if
padding is disabled, or when decrypting, the total number of bytes does
have to be aligned to the block size; otherwise CCCryptFinal() will
return kCCAlignmentError.
A general rule for the size of the output buffer which must be provided
by the caller is that for block ciphers, the output length is never
larger than the input length plus the block size. For stream ciphers,
the output length is always exactly the same as the input length. See the
discussion for CCCryptorGetOutputLength() for more information on this
topic.
CCCryptFinal() finishes encryption and decryption operations and obtains
the final data output. Except when kCCBufferTooSmall is returned, the
CCCryptorRef can no longer be used for subsequent operations unless
CCCryptorReset() is called on it.
It is not necessary to call CCCryptorFinal() when performing symmetric
encryption or decryption if padding is disabled, or when using a stream
cipher.
It is not necessary to call CCCryptorFinal() prior to CCCryptorRelease()
when aborting an operation.
Use CCCryptorGetOutputLength() to determine output buffer size required
to process a given input size. Some general rules apply that allow
clients of this module to know a priori how much output buffer space will
be required in a given situation. For stream ciphers, the output size is
always equal to the input size, and CCCryptorFinal() never produces any
data. For block ciphers, the output size will always be less than or
equal to the input size plus the size of one block. For block ciphers, if
the input size provided to each call to CCCryptorUpdate() is is an inte-
gral multiple of the block size, then the output size for each call to
CCCryptorUpdate() is less than or equal to the input size for that call
to CCCryptorUpdate(). CCCryptorFinal() only produces output when using a
block cipher with padding enabled.
CCCryptorReset() reinitializes an existing CCCryptorRef with a (possibly)
new initialization vector. The key contained in the CCCryptorRef is
unchanged. This function is not implemented for stream ciphers. This can
be called on a CCCryptorRef with data pending (i.e. in a padded mode
operation before CCCryptFinal() is called); however any pending data will
be lost in that case.
CCCrypt() is a stateless, one-shot encrypt or decrypt operation. This
basically performs a sequence of CCCrytorCreate(), CCCryptorUpdate(),
CCCryptorFinal(), and CCCryptorRelease().
RETURN VALUES
The following values may be returned as a status of type CCCryptorStatus.
kCCSuccess - Operation completed normally.
kCCParamError - Illegal parameter value.
kCCBufferTooSmall - Insufficent buffer provided for specified operation.
kCCMemoryFailure - Memory allocation failure.
kCCAlignmentError - Input size was not aligned properly.
kCCDecodeError - Input data did not decode or decrypt properly.
kCCUnimplemented - Function not implemented for the current algorithm.
SEE ALSO
CCHmac(3), CC_MD5(3), CC_SHA(3), CC_crypto(3)
STANDARDS
AES: Federal Information Processing Standard FIPS PUB 197
(Advanced Encryption Standard),
DES: Federal Information Processing Standard FIPS PUB 46-3 (Data
Encryption Standard)
3DES: NIST Special PublicationPUB 800-67 (Recommendation for the
Triple Data Encryption Algorithm (TDEA) Block Cipher)
BSD March 22, 2007 BSD
Mac OS X 10.6 - Generated Thu Sep 17 20:10:52 CDT 2009