EVPBytesToKey(3) OpenSSL EVPBytesToKey(3)

NAME
       EVPBytesToKey - password based encryption routine

SYNOPSIS
        #include 

        int EVPBytesToKey(const EVPCIPHER *type,const EVPMD *md,
                              const unsigned char *salt,
                              const unsigned char *data, int datal, int count,
                              unsigned char *key,unsigned char *iv);

DESCRIPTION
       EVPBytesToKey() derives a key and IV from various parameters. ttyyppee is
       the cipher to derive the key and IV for. mmdd is the message digest to
       use.  The ssaalltt paramter is used as a salt in the derivation: it should
       point to an 8 byte buffer or NULL if no salt is used. ddaattaa is a buffer
       containing ddaattaall bytes which is used to derive the keying data. ccoouunntt
       is the iteration count to use. The derived key and IV will be written
       to kkeeyy and iivv respectively.

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

       Increasing the ccoouunntt 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 MMDD55
       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.

KKEEYY DDEERRIIVVAATTIIOONN AALLGGOORRIITTHHMM
       The key and IV is derived by concatenating D1, D2, etc until enough
       data is available for the key and IV. Di is defined as:

               Di = HASH^count(D(i-1) || data || salt)

       where || denotes concatentaion, D0 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
       EVPBytesToKey() returns the size of the derived key in bytes.

SEE ALSO
       evp(3), rand(3), EVPEncryptInit(3),

HISTORY
0.9.7l                            2003-09-30                 EVPBytesToKey(3)