BF_SET_KEY(3) | Library Functions Manual | BF_SET_KEY(3)

# NAME

`BF_set_key`, `BF_encrypt`, `BF_decrypt`, `BF_ecb_encrypt`, `BF_cbc_encrypt`, `BF_cfb64_encrypt`, `BF_ofb64_encrypt` — Blowfish encryption

# SYNOPSIS

library “libcrypto”
`#include <openssl/blowfish.h>`

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

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

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

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);

# DESCRIPTION

This library implements the Blowfish cipher, which was invented and defined by Counterpane. Note that applications should use higher level functions such as EVP_EncryptInit(3) instead of calling the Blowfish functions directly.

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 and 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 a 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-bit 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 implementing `modes' of Blowfish. The alternative is to use `BF_ecb_encrypt`(). Be aware that these functions take each 32-bit chunk in host-byte order, which is little-endian on little-endian platforms and big-endian on big-endian ones.

# SEE ALSO

EVP_EncryptInit(3)

# HISTORY

`BF_set_key`(), `BF_encrypt`(), `BF_ecb_encrypt`(), `BF_cbc_encrypt`(), `BF_cfb64_encrypt`(), and `BF_ofb64_encrypt`() first appeared in SSLeay 0.6.6. `BF_decrypt`() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.

June 8, 2025 | Debian