BF_SET_KEY(3)

💖 BF_SET_KEY(3) — Blowfish encryption 💖

okay so bestie, welcome to the Blowfish page 💅 this is part of the libcrypto library, and honestly it's giving "vintage crypto baddie" energy. Let's get into it.

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✨ SYNOPSIS ✨

#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);

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🌸 DESCRIPTION 🌸

So this library implements the Blowfish cipher — it was invented and defined by Counterpane, and it's lowkey a legend. 🐡

🫶 Real talk though: applications should use higher level functions such as EVP_EncryptInit(3) instead of calling the Blowfish functions directly. Like, no cap — that's the move.

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. Two-step era. 💫

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🎀 the key setup

BF_set_key() sets up the BF_KEY key using the len bytes long key at data. That's it, that's the vibe check.

🔥 the basic one

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 — she simply does not care about the rest.

🦋 the mode girlies

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. 😭 Like, that's the whole thing. Some programs and protocols simplify this, like SSH, where ivec is simply initialized to zero. Slay for simplicity.

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. Not optional, bestie. 🫶

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💅 BF_cbc_encrypt

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. main character ivec. 👑

⭐ BF_cfb64_encrypt

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

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. copy-paste energy but make it cipher. ✨

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💀 the scary low-level ones

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().

🙈 Heads up, bestie: 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. So your bytes are doing whatever your machine's endianness says, and that's a real "it's giving portability chaos" moment. 🔥

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🔍 SEE ALSO 🔍

• EVP_EncryptInit(3) — the grown-up way to do this, fr fr

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👑 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. ancient. iconic. still here. 🏛️

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mwah 💋 this page is from the Debian build, dated June 8, 2025, and it's the BF_SET_KEY(3) entry — go forth and encrypt responsibly, bestie 🫶