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 paramter 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