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Title "EVP_BYTESTOKEY 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
EVP_BytesToKey - password based encryption routine Header "SYNOPSIS" .Vb 1 #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); .Ve Header "DESCRIPTION" \fBEVP_BytesToKey() derives a key and \s-1IV\s0 from various parameters. type is the cipher to derive the key and \s-1IV\s0 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 \s-1NULL\s0 if no salt is used. data is a buffer containing \fBdatal bytes which is used to derive the keying data. count is the iteration count to use. The derived key and \s-1IV\s0 will be written to key and iv respectively. Header "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 perform a brute force attack using a large number of candidate passwords.

If the total key and \s-1IV\s0 length is less than the digest length and \fB\s-1MD5\s0 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 \s-1PBKDF2\s0 as defined in PKCS#5v2.1 and provided by \s-1PKCS5_PBKDF2_HMAC.\s0

Header "KEY DERIVATION ALGORITHM" The key and \s-1IV\s0 is derived by concatenating D_1, D_2, etc until enough data is available for the key and \s-1IV.\s0 D_i is defined as:

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

where || denotes concatenation, D_0 is empty, \s-1HASH\s0 is the digest algorithm in use, HASH^1(data) is simply \s-1HASH\s0(data), HASH^2(data) is \s-1HASH\s0(\s-1HASH\s0(data)) and so on.

The initial bytes are used for the key and the subsequent bytes for the \s-1IV.\s0

Header "RETURN VALUES" If data is \s-1NULL,\s0 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. Header "SEE ALSO" \fBevp\|(7), RAND_bytes\|(3), \s-1PKCS5_PBKDF2_HMAC\s0\|(3), \fBEVP_EncryptInit\|(3) Header "COPYRIGHT" Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.