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5.2 Available cipher modes

GCRY_CIPHER_MODE_NONE
No mode specified. This should not be used. The only exception is that if Libgcrypt is not used in FIPS mode and if any debug flag has been set, this mode may be used to bypass the actual encryption.
GCRY_CIPHER_MODE_ECB
Electronic Codebook mode.
GCRY_CIPHER_MODE_CFB
Cipher Feedback mode. The shift size equals the block size of the cipher (e.g. for AES it is CFB-128).
GCRY_CIPHER_MODE_CBC
Cipher Block Chaining mode.
GCRY_CIPHER_MODE_STREAM
Stream mode, only to be used with stream cipher algorithms.
GCRY_CIPHER_MODE_OFB
Output Feedback mode.
GCRY_CIPHER_MODE_CTR
Counter mode.
GCRY_CIPHER_MODE_AESWRAP
This mode is used to implement the AES-Wrap algorithm according to RFC-3394. It may be used with any 128 bit block length algorithm, however the specs require one of the 3 AES algorithms. These special conditions apply: If gcry_cipher_setiv has not been used the standard IV is used; if it has been used the lower 64 bit of the IV are used as the Alternative Initial Value. On encryption the provided output buffer must be 64 bit (8 byte) larger than the input buffer; in-place encryption is still allowed. On decryption the output buffer may be specified 64 bit (8 byte) shorter than then input buffer. As per specs the input length must be at least 128 bits and the length must be a multiple of 64 bits.
GCRY_CIPHER_MODE_CCM
Counter with CBC-MAC mode is an Authenticated Encryption with Associated Data (AEAD) block cipher mode, which is specified in 'NIST Special Publication 800-38C' and RFC 3610.
GCRY_CIPHER_MODE_GCM
Galois/Counter Mode (GCM) is an Authenticated Encryption with Associated Data (AEAD) block cipher mode, which is specified in 'NIST Special Publication 800-38D'.