EVP_BytesToKey(3)

EVP_BytesToKey(3)            OpenSSL            EVP_BytesToKey(3)

NAME

     EVP_BytesToKey - password based encryption routine

SYNOPSIS

      #include <openssl/evp.h>

      int EVP_BytesToKey(const EVP_CIPHER *type,const EVP_MD *md,
                            const unsigned char *salt,
                            const unsigned char *data, int datal, int count,
                            unsigned char *key,unsigned char *iv);

DESCRIPTION

     EVP_BytesToKey() derives a key and IV from various
     parameters. type is the cipher to derive the key and IV for.
     md is the message digest to use.  The salt parameter is used
     as a salt in the derivation: it should point to an 8 byte
     buffer or NULL if no salt is used. data is a buffer
     containing datal bytes which is used to derive the keying
     data. count is the iteration count to use. The derived key
     and IV will be written to key and iv respectively.

NOTES

     A typical application of this function is to derive keying
     material for an encryption algorithm from a password in the
     data parameter.

     Increasing the count parameter slows down the algorithm
     which makes it harder for an attacker to peform a brute
     force attack using a large number of candidate passwords.

     If the total key and IV length is less than the digest
     length and MD5 is used then the derivation algorithm is
     compatible with PKCS#5 v1.5 otherwise a non standard
     extension is used to derive the extra data.

     Newer applications should use a more modern algorithm such
     as PBKDF2 as defined in PKCS#5v2.1 and provided by
     PKCS5_PBKDF2_HMAC.

KEY DERIVATION ALGORITHM

     The key and IV is derived by concatenating D_1, D_2, etc
     until enough data is available for the key and IV. D_i is
     defined as:

             D_i = HASH^count(D_(i-1) || data || salt)

     where || denotes concatentaion, D_0 is empty, HASH is the
     digest algorithm in use, HASH^1(data) is simply HASH(data),
     HASH^2(data) is HASH(HASH(data)) and so on.

     The initial bytes are used for the key and the subsequent
     bytes for the IV.

1.0.2t               Last change: 2019-09-10                    1

EVP_BytesToKey(3)            OpenSSL            EVP_BytesToKey(3)

RETURN VALUES

     If data is NULL, then EVP_BytesToKey() returns the number of
     bytes needed to store the derived key.  Otherwise,
     EVP_BytesToKey() returns the size of the derived key in
     bytes, or 0 on error.

SEE ALSO

     evp(3), rand(3), EVP_EncryptInit(3)

HISTORY

1.0.2t               Last change: 2019-09-10                    2