EVP_BytesToKey
Section: OpenSSL (3)
Updated: 2017-05-25
Index
Return to Main Contents
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 a more modern algorithm such as PBKDF2 as
defined in PKCS#5v2.1 and provided by PKCS5_PBKDF2_HMAC.
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
If
data is
NULL, 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.
SEE ALSO
evp(3),
rand(3),
EVP_EncryptInit(3)
HISTORY
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- NOTES
-
- KEY DERIVATION ALGORITHM
-
- RETURN VALUES
-
- SEE ALSO
-
- HISTORY
-
|
|
- Running on 
-
:
: 