Manual Pages for UNIX Operating System command usage for man EVP_BytesToKey

OpenSSL                                  EVP_BytesToKey(3openssl)



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     EVP_BytesToKey - password based encryption routine

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      #include 

      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);


DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     EVP_BytesToKey() derives a key and IV from various
     parameters. ttttyyyyppppeeee is the cipher to derive the key and IV for.
     mmmmdddd is the message digest to use.  The ssssaaaalllltttt paramter is used
     as a salt in the derivation: it should point to an 8 byte
     buffer or NULL if no salt is used. ddddaaaattttaaaa is a buffer
     containing ddddaaaattttaaaallll bytes which is used to derive the keying
     data. ccccoooouuuunnnntttt is the iteration count to use. The derived key
     and IV will be written to kkkkeeeeyyyy and iiiivvvv respectively.

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

     Increasing the ccccoooouuuunnnntttt 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 MMMMDDDD5555 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.

KKKKEEEEYYYY DDDDEEEERRRRIIIIVVVVAAAATTTTIIIIOOOONNNN AAAALLLLGGGGOOOORRRRIIIITTTTHHHHMMMM
     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.



25/Nov/2004            Last change: 0.9.8o                      1






OpenSSL                                  EVP_BytesToKey(3openssl)



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

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

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25/Nov/2004            Last change: 0.9.8o                      2