AES_ENCRYPT(3) | Library Functions Manual | AES_ENCRYPT(3)

# NAME

`AES_set_encrypt_key`, `AES_set_decrypt_key`, `AES_encrypt`, `AES_decrypt`, `AES_cbc_encrypt` — low-level interface to the AES symmetric cipher

# SYNOPSIS

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

int
`AES_set_encrypt_key`(const unsigned char *userKey, const int bits, AES_KEY *key);

int
`AES_set_decrypt_key`(const unsigned char *userKey, const int bits, AES_KEY *key);

void
`AES_encrypt`(const unsigned char *in, unsigned char *out, const AES_KEY *key);

void
`AES_decrypt`(const unsigned char *in, unsigned char *out, const AES_KEY *key);

void
`AES_cbc_encrypt`(const unsigned char *in, unsigned char *out, size_t length, const AES_KEY *key, unsigned char *ivec, const int enc);

# DESCRIPTION

These function provide a low-level interface to the AES symmetric cipher algorithm, also called Rijndael. For reasons of flexibility, it is recommended that application programs use the high-level interface described in EVP_EncryptInit(3) and EVP_aes_128_cbc(3) instead whenever possible.

AES_KEY is a structure that can hold up to 60 int values and a number of rounds.

`AES_set_encrypt_key`() expands the userKey, which is bits long, into the key structure to prepare for encryption. The number of bits and bytes read from userKey, the number of int values stored into key, and the number of rounds are as follows:

bits | bytes | ints | rounds
128 | 16 | 44 | 10
192 | 24 | 52 | 12
256 | 32 | 60 | 14

`AES_set_decrypt_key`() does the same, but in preparation for decryption.

`AES_encrypt`() reads a single 16 byte block from *in, encrypts it with the key, and writes the 16 resulting bytes to *out. The 16 byte buffers starting at in and out can overlap, and in and out can even point to the same memory location.

`AES_decrypt`() decrypts a single block and is otherwise identical to `AES_encrypt`().

If enc is non-zero, `AES_cbc_encrypt`() encrypts len bytes at in to out using the 128 bit key and the 128 bit initialization vector ivec in CBC mode. If enc is 0, `AES_cbc_encrypt`() performs the corresponding decryption.

# RETURN VALUES

`AES_set_encrypt_key`() and `AES_set_decrypt_key`() return 0 for success, -1 if userKey or key is `NULL`, or -2 if the number of bits is unsupported.

# SEE ALSO

crypto(3), EVP_aes_128_cbc(3), EVP_EncryptInit(3)

# STANDARDS

ISO/IEC 18033-3:2010 Information technology — Security techniques — Encryption algorithms — Part 3: Block ciphers

# HISTORY

These functions first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2.

# AUTHORS

Vincent Rijmen
Antoon Bosselaers
Paulo Barreto

June 8, 2025 | Debian