evp_encryptinit.pod

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EVP_CIPHER_CTX_ctrl() allows various cipher specific parameters to be determined
and set. Currently only the RC2 effective key length and the number of rounds of
RC5 can be set.

=head1 RETURN VALUES

EVP_EncryptInit(), EVP_EncryptUpdate() and EVP_EncryptFinal() return 1 for success
and 0 for failure.

EVP_DecryptInit() and EVP_DecryptUpdate() return 1 for success and 0 for failure.
EVP_DecryptFinal() returns 0 if the decrypt failed or 1 for success.

EVP_CipherInit() and EVP_CipherUpdate() return 1 for success and 0 for failure.
EVP_CipherFinal() returns 1 for a decryption failure or 1 for success.

EVP_CIPHER_CTX_cleanup() returns 1 for success and 0 for failure.

EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
return an B<EVP_CIPHER> structure or NULL on error.

EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID.

EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block
size.

EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
length.

EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
length or zero if the cipher does not use an IV.

EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the cipher's
OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT IDENTIFIER.

EVP_CIPHER_CTX_cipher() returns an B<EVP_CIPHER> structure.

EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return 1 for 
success or zero for failure.

=head1 CIPHER LISTING

All algorithms have a fixed key length unless otherwise stated.

=over 4

=item EVP_enc_null()

Null cipher: does nothing.

=item EVP_des_cbc(void), EVP_des_ecb(void), EVP_des_cfb(void), EVP_des_ofb(void)

DES in CBC, ECB, CFB and OFB modes respectively. 

=item EVP_des_ede_cbc(void), EVP_des_ede(), EVP_des_ede_ofb(void),  EVP_des_ede_cfb(void)

Two key triple DES in CBC, ECB, CFB and OFB modes respectively.

=item EVP_des_ede3_cbc(void), EVP_des_ede3(), EVP_des_ede3_ofb(void),  EVP_des_ede3_cfb(void)

Three key triple DES in CBC, ECB, CFB and OFB modes respectively.

=item EVP_desx_cbc(void)

DESX algorithm in CBC mode.

=item EVP_rc4(void)

RC4 stream cipher. This is a variable key length cipher with default key length 128 bits.

=item EVP_rc4_40(void)

RC4 stream cipher with 40 bit key length. This is obsolete and new code should use EVP_rc4()
and the EVP_CIPHER_CTX_set_key_length() function.

=item EVP_idea_cbc() EVP_idea_ecb(void), EVP_idea_cfb(void), EVP_idea_ofb(void), EVP_idea_cbc(void)

IDEA encryption algorithm in CBC, ECB, CFB and OFB modes respectively.

=item EVP_rc2_cbc(void), EVP_rc2_ecb(void), EVP_rc2_cfb(void), EVP_rc2_ofb(void)

RC2 encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key
length cipher with an additional parameter called "effective key bits" or "effective key length".
By default both are set to 128 bits.

=item EVP_rc2_40_cbc(void), EVP_rc2_64_cbc(void)

RC2 algorithm in CBC mode with a default key length and effective key length of 40 and 64 bits.
These are obsolete and new code should use EVP_rc2_cbc(), EVP_CIPHER_CTX_set_key_length() and
EVP_CIPHER_CTX_ctrl() to set the key length and effective key length.

=item EVP_bf_cbc(void), EVP_bf_ecb(void), EVP_bf_cfb(void), EVP_bf_ofb(void);

Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key
length cipher.

=item EVP_cast5_cbc(void), EVP_cast5_ecb(void), EVP_cast5_cfb(void), EVP_cast5_ofb(void)

CAST encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key
length cipher.

=item EVP_rc5_32_12_16_cbc(void), EVP_rc5_32_12_16_ecb(void), EVP_rc5_32_12_16_cfb(void), EVP_rc5_32_12_16_ofb(void)

RC5 encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length
cipher with an additional "number of rounds" parameter. By default the key length is set to 128
bits and 12 rounds.

=back

=head1 NOTES

Where possible the B<EVP> interface to symmetric ciphers should be used in
preference to the low level interfaces. This is because the code then becomes
transparent to the cipher used and much more flexible.

PKCS padding works by adding B<n> padding bytes of value B<n> to make the total 
length of the encrypted data a multiple of the block size. Padding is always
added so if the data is already a multiple of the block size B<n> will equal
the block size. For example if the block size is 8 and 11 bytes are to be
encrypted then 5 padding bytes of value 5 will be added.

When decrypting the final block is checked to see if it has the correct form.

Although the decryption operation can produce an error, it is not a strong
test that the input data or key is correct. A random block has better than
1 in 256 chance of being of the correct format and problems with the
input data earlier on will not produce a final decrypt error.

The functions EVP_EncryptInit(), EVP_EncryptUpdate(), EVP_EncryptFinal(),
EVP_DecryptInit(), EVP_DecryptUpdate(), EVP_CipherInit() and EVP_CipherUpdate()
and EVP_CIPHER_CTX_cleanup() did not return errors in OpenSSL version 0.9.5a or
earlier. Software only versions of encryption algorithms will never return
error codes for these functions, unless there is a programming error (for example
and attempt to set the key before the cipher is set in EVP_EncryptInit() ).

=head1 BUGS

For RC5 the number of rounds can currently only be set to 8, 12 or 16. This is
a limitation of the current RC5 code rather than the EVP interface.

It should be possible to disable PKCS padding: currently it isn't.

EVP_MAX_KEY_LENGTH and EVP_MAX_IV_LENGTH only refer to the internal ciphers with
default key lengths. If custom ciphers exceed these values the results are
unpredictable. This is because it has become standard practice to define a 
generic key as a fixed unsigned char array containing EVP_MAX_KEY_LENGTH bytes.

The ASN1 code is incomplete (and sometimes inaccurate) it has only been tested
for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC mode.

=head1 EXAMPLES

Get the number of rounds used in RC5:

 int nrounds;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC5_ROUNDS, 0, &i);

Get the RC2 effective key length:

 int key_bits;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC2_KEY_BITS, 0, &i);

Set the number of rounds used in RC5:

 int nrounds;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC5_ROUNDS, i, NULL);

Set the number of rounds used in RC2:

 int nrounds;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC2_KEY_BITS, i, NULL);

=head1 SEE ALSO

L<evp(3)|evp(3)>

=head1 HISTORY

=cut