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blowfish

Section: OpenSSL (3)
Updated: 2017-05-25
Index Return to Main Contents

NAME

blowfish, BF_set_key, BF_encrypt, BF_decrypt, BF_ecb_encrypt, BF_cbc_encrypt, BF_cfb64_encrypt, BF_ofb64_encrypt, BF_options - Blowfish encryption

SYNOPSIS

 #include <openssl/blowfish.h>

 void BF_set_key(BF_KEY *key, int len, const unsigned char *data);

 void BF_ecb_encrypt(const unsigned char *in, unsigned char *out,
         BF_KEY *key, int enc);
 void BF_cbc_encrypt(const unsigned char *in, unsigned char *out,
         long length, BF_KEY *schedule, unsigned char *ivec, int enc);
 void BF_cfb64_encrypt(const unsigned char *in, unsigned char *out,
         long length, BF_KEY *schedule, unsigned char *ivec, int *num,
         int enc);
 void BF_ofb64_encrypt(const unsigned char *in, unsigned char *out,
         long length, BF_KEY *schedule, unsigned char *ivec, int *num);
 const char *BF_options(void);

 void BF_encrypt(BF_LONG *data,const BF_KEY *key);
 void BF_decrypt(BF_LONG *data,const BF_KEY *key);

DESCRIPTION

This library implements the Blowfish cipher, which was invented and described by Counterpane (see http://www.counterpane.com/blowfish.html ).

Blowfish is a block cipher that operates on 64 bit (8 byte) blocks of data. It uses a variable size key, but typically, 128 bit (16 byte) keys are considered good for strong encryption. Blowfish can be used in the same modes as DES (see des_modes(7)). Blowfish is currently one of the faster block ciphers. It is quite a bit faster than DES, and much faster than IDEA or RC2.

Blowfish consists of a key setup phase and the actual encryption or decryption phase.

BF_set_key() sets up the BF_KEY key using the len bytes long key at data.

BF_ecb_encrypt() is the basic Blowfish encryption and decryption function. It encrypts or decrypts the first 64 bits of in using the key key, putting the result in out. enc decides if encryption (BF_ENCRYPT) or decryption (BF_DECRYPT) shall be performed. The vector pointed at by in and out must be 64 bits in length, no less. If they are larger, everything after the first 64 bits is ignored.

The mode functions BF_cbc_encrypt(), BF_cfb64_encrypt() and BF_ofb64_encrypt() all operate on variable length data. They all take an initialization vector ivec which needs to be passed along into the next call of the same function for the same message. ivec may be initialized with anything, but the recipient needs to know what it was initialized with, or it won't be able to decrypt. Some programs and protocols simplify this, like SSH, where ivec is simply initialized to zero. BF_cbc_encrypt() operates on data that is a multiple of 8 bytes long, while BF_cfb64_encrypt() and BF_ofb64_encrypt() are used to encrypt an variable number of bytes (the amount does not have to be an exact multiple of 8). The purpose of the latter two is to simulate stream ciphers, and therefore, they need the parameter num, which is a pointer to an integer where the current offset in ivec is stored between calls. This integer must be initialized to zero when ivec is initialized.

BF_cbc_encrypt() is the Cipher Block Chaining function for Blowfish. It encrypts or decrypts the 64 bits chunks of in using the key schedule, putting the result in out. enc decides if encryption (BF_ENCRYPT) or decryption (BF_DECRYPT) shall be performed. ivec must point at an 8 byte long initialization vector.

BF_cfb64_encrypt() is the CFB mode for Blowfish with 64 bit feedback. It encrypts or decrypts the bytes in in using the key schedule, putting the result in out. enc decides if encryption (BF_ENCRYPT) or decryption (BF_DECRYPT) shall be performed. ivec must point at an 8 byte long initialization vector. num must point at an integer which must be initially zero.

BF_ofb64_encrypt() is the OFB mode for Blowfish with 64 bit feedback. It uses the same parameters as BF_cfb64_encrypt(), which must be initialized the same way.

BF_encrypt() and BF_decrypt() are the lowest level functions for Blowfish encryption. They encrypt/decrypt the first 64 bits of the vector pointed by data, using the key key. These functions should not be used unless you implement 'modes' of Blowfish. The alternative is to use BF_ecb_encrypt(). If you still want to use these functions, you should be aware that they take each 32-bit chunk in host-byte order, which is little-endian on little-endian platforms and big-endian on big-endian ones.