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67 lines
2.1 KiB
67 lines
2.1 KiB
=pod |
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=head1 NAME |
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EVP_BytesToKey - password based encryption routine |
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=head1 SYNOPSIS |
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#include <openssl/evp.h> |
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int EVP_BytesToKey(const EVP_CIPHER *type,const EVP_MD *md, |
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const unsigned char *salt, |
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const unsigned char *data, int datal, int count, |
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unsigned char *key,unsigned char *iv); |
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=head1 DESCRIPTION |
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EVP_BytesToKey() derives a key and IV from various parameters. B<type> is |
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the cipher to derive the key and IV for. B<md> is the message digest to use. |
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The B<salt> parameter is used as a salt in the derivation: it should point to |
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an 8 byte buffer or NULL if no salt is used. B<data> is a buffer containing |
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B<datal> bytes which is used to derive the keying data. B<count> is the |
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iteration count to use. The derived key and IV will be written to B<key> |
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and B<iv> respectively. |
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=head1 NOTES |
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A typical application of this function is to derive keying material for an |
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encryption algorithm from a password in the B<data> parameter. |
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Increasing the B<count> parameter slows down the algorithm which makes it |
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harder for an attacker to peform a brute force attack using a large number |
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of candidate passwords. |
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If the total key and IV length is less than the digest length and |
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B<MD5> is used then the derivation algorithm is compatible with PKCS#5 v1.5 |
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otherwise a non standard extension is used to derive the extra data. |
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Newer applications should use more standard algorithms such as PKCS#5 |
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v2.0 for key derivation. |
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=head1 KEY DERIVATION ALGORITHM |
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The key and IV is derived by concatenating D_1, D_2, etc until |
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enough data is available for the key and IV. D_i is defined as: |
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D_i = HASH^count(D_(i-1) || data || salt) |
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where || denotes concatentaion, D_0 is empty, HASH is the digest |
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algorithm in use, HASH^1(data) is simply HASH(data), HASH^2(data) |
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is HASH(HASH(data)) and so on. |
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The initial bytes are used for the key and the subsequent bytes for |
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the IV. |
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=head1 RETURN VALUES |
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EVP_BytesToKey() returns the size of the derived key in bytes. |
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=head1 SEE ALSO |
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L<evp(3)|evp(3)>, L<rand(3)|rand(3)>, |
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L<EVP_EncryptInit(3)|EVP_EncryptInit(3)> |
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=head1 HISTORY |
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=cut
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