Update docs.

EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()

return an B<EVP_MD> structure when passed a digest name, a digest NID or

and ASN1_OBJECT structure respectively. The digest table must be initialised

an ASN1_OBJECT structure respectively. The digest table must be initialised

using, for example, OpenSSL_add_all_digests() for these functions to work.

=head1 RETURN VALUES

EVP_MD_CTX_block_size()	and EVP_MD_block_size() return the digest or block

size in bytes.

EVP_md_null(), EVP_MD *EVP_md2(), EVP_MD *EVP_md5(), EVP_MD *EVP_sha(),

EVP_sha1(), EVP_dss(), EVP_dss1(), EVP_mdc2() and EVP_ripemd160() return

pointers to the corresponding EVP_MD structures.

EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_dss(),

EVP_dss1(), EVP_mdc2() and EVP_ripemd160() return pointers to the

corresponding EVP_MD structures.

EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()

return either an B<EVP_MD> structure or NULL if an error occurs.

L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,

L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,

L<sha(3)|sha(3)>

L<sha(3)|sha(3)>, L<digest(1)|digest(1)>

=head1 HISTORY

 #define EVP_CIPHER_CTX_iv_length(e)	((e)->cipher->iv_len)

 #define EVP_CIPHER_CTX_type(c)         EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c))

 int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type);

 int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type);

=head1 DESCRIPTION

The EVP cipher routines are a high level interface to certain

with cipher B<type>. B<type> is normally supplied by a function such

as EVP_des_cbc() . B<key> is the symmetric key to use and B<iv> is the

IV to use (if necessary), the actual number of bytes used for the

key and IV depends on the cipher.

key and IV depends on the cipher. It is possible to set all parameters

to NULL except B<type> in an initial call and supply the remaining

parameters in subsequent calls. This is normally done when the 

EVP_CIPHER_asn1_to_param() function is called to set the cipher

parameters from an ASN1 AlgorithmIdentifier and the key from a

different source.

EVP_EncryptUpdate() encrypts B<inl> bytes from the buffer B<in> and

writes the encrypted version to B<out>. This function can be called

It should be called after all operations using a cipher are complete

so sensitive information does not remain in memory.

EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()

return an EVP_CIPHER structure when passed a cipher name, a NID or an

ASN1_OBJECT structure.

EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return the NID of a cipher when

passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> structure.  The actual NID

value is an internal value which may not have a corresponding OBJECT

IDENTIFIER.

EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key

length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>

structure. The constant B<EVP_MAX_KEY_LENGTH> is the maximum key length

for all ciphers.

EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV

length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>.

It will return zero if the cipher does not use an IV.  The constant

B<EVP_MAX_IV_LENGTH> is the maximum IV length for all ciphers.

EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block

size of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>

structure. The constant B<EVP_MAX_IV_LENGTH> is also the maximum block

length for all ciphers.

EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the type of the passed

cipher or context. This "type" is the actual NID of the cipher OBJECT

IDENTIFIER as such it ignores the cipher parameters and 40 bit RC2 and

128 bit RC2 have the same NID.

EVP_CIPHER_CTX_cipher() returns the B<EVP_CIPHER> structure when passed

an B<EVP_CIPHER_CTX> structure.

EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter" based

on the passed cipher. This will typically include any parameters and an

IV. The cipher IV (if any) must be set when this call is made. This call

should be made before the cipher is actually "used" (before any

EVP_EncryptUpdate(), EVP_DecryptUpdate() calls for example). This function

may fail if the cipher does not have any ASN1 support.

EVP_CIPHER_asn1_to_param() sets the cipher parameters based on an ASN1

AlgorithmIdentifier "parameter". The precise effect depends on the cipher

In the case of RC2, for example, it will set the IV and effective key length.

This function should be called after the base cipher type is set but before

the key is set. For example EVP_CipherInit() will be called with the IV and

key set to NULL, EVP_CIPHER_asn1_to_param() will be called and finally

EVP_CipherInit() again with all parameters except the key set to NULL. It is

possible for this function to fail if the cipher does not have any ASN1 support

or the parameters cannot be set (for example the RC2 effective key length

does not have an B<EVP_CIPHER> structure).

=head1 RETURN VALUES

EVP_EncryptInit(), EVP_EncryptUpdate() and EVP_EncryptFinal() do not return

EVP_CipherFinal() returns 1 for a decryption failure or 1 for success, if

the operation is encryption then it always returns 1.

EVP_CIPHER_CTX_cleanup() does not return a value.

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.

=head1 NOTES

Where possible the B<EVP> interface to symmetric ciphers should be used in