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 more standard algorithms such as PKCS#5 v2.0 for key
       derivation.

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.

RETURN VALUES

       EVP_BytesToKey() returns the size of the derived key in bytes.

SEE ALSO

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

HISTORY