The EVP library provides a high-level interface to cryptographic
functions.
-B<EVP_Seal>I<...> and B<EVP_Open>I<...> provide public key encryption
-and decryption to implement digital "envelopes".
+L<B<EVP_Seal>I<...>|EVP_SealInit(3)> and L<B<EVP_Open>I<...>|EVP_OpenInit(3)>
+provide public key encryption and decryption to implement digital "envelopes".
-The B<EVP_Sign>I<...> and B<EVP_Verify>I<...> functions implement
-digital signatures.
+The L<B<EVP_DigestSign>I<...>|EVP_DigestSignInit(3)> and
+L<B<EVP_DigestVerify>I<...>|EVP_DigestVerifyInit(3)> functions implement
+digital signatures and Message Authentication Codes (MACs). Also see the older
+L<B<EVP_Sign>I<...>|EVP_SignInit(3)> and L<B<EVP_Verify>I<...>|EVP_VerifyInit(3)>
+functions.
+
+Symmetric encryption is available with the L<B<EVP_Encrypt>I<...>|EVP_EncryptInit(3)>
+functions. The L<B<EVP_Digest>I<...>|EVP_DigestInit(3)> functions provide message digests.
+
+The B<EVP_PKEY>I<...> functions provide a high level interface to
+asymmetric algorithms. To create a new EVP_PKEY see
+L<EVP_PKEY_new(3)>. EVP_PKEYs can be associated
+with a private key of a particular algorithm by using the functions
+described on the L<EVP_PKEY_set1_RSA(3)> page, or
+new keys can be generated using L<EVP_PKEY_keygen(3)>.
+EVP_PKEYs can be compared using L<EVP_PKEY_cmp(3)>, or printed using
+L<EVP_PKEY_print_private(3)>.
+
+The EVP_PKEY functions support the full range of asymmetric algorithm operations:
+
+=over
+
+=item For key agreement see L<EVP_PKEY_derive(3)>
+
+=item For signing and verifying see L<EVP_PKEY_sign(3)>,
+L<EVP_PKEY_verify(3)> and L<EVP_PKEY_verify_recover(3)>.
+However, note that
+these functions do not perform a digest of the data to be signed. Therefore
+normally you would use the L<EVP_DigestSignInit(3)>
+functions for this purpose.
+
+=item For encryption and decryption see L<EVP_PKEY_encrypt(3)>
+and L<EVP_PKEY_decrypt(3)> respectively. However, note that
+these functions perform encryption and decryption only. As public key
+encryption is an expensive operation, normally you would wrap
+an encrypted message in a "digital envelope" using the L<EVP_SealInit(3)> and
+L<EVP_OpenInit(3)> functions.
+
+=back
-Symmetric encryption is available with the B<EVP_Encrypt>I<...>
-functions. The B<EVP_Digest>I<...> functions provide message digests.
+The L<EVP_BytesToKey(3)> function provides some limited support for password
+based encryption. Careful selection of the parameters will provide a PKCS#5 PBKDF1 compatible
+implementation. However, new applications should not typically use this (preferring, for example,
+PBKDF2 from PCKS#5).
-Algorithms are loaded with OpenSSL_add_all_algorithms(3).
+All the symmetric algorithms (ciphers), digests and asymmetric algorithms
+(public key algorithms) can be replaced by L<engine(3)> modules providing alternative
+implementations. If ENGINE implementations of ciphers or digests are registered
+as defaults, then the various EVP functions will automatically use those
+implementations automatically in preference to built in software
+implementations. For more information, consult the engine(3) man page.
-All the symmetric algorithms (ciphers) and digests can be replaced by ENGINE
-modules providing alternative implementations. If ENGINE implementations of
-ciphers or digests are registered as defaults, then the various EVP functions
-will automatically use those implementations automatically in preference to
-built in software implementations. For more information, consult the engine(3)
-man page.
+Although low level algorithm specific functions exist for many algorithms
+their use is discouraged. They cannot be used with an ENGINE and ENGINE
+versions of new algorithms cannot be accessed using the low level functions.
+Also makes code harder to adapt to new algorithms and some options are not
+cleanly supported at the low level and some operations are more efficient
+using the high level interface.
=head1 SEE ALSO
-L<EVP_DigestInit(3)|EVP_DigestInit(3)>,
-L<EVP_EncryptInit(3)|EVP_EncryptInit(3)>,
-L<EVP_OpenInit(3)|EVP_OpenInit(3)>,
-L<EVP_SealInit(3)|EVP_SealInit(3)>,
-L<EVP_SignInit(3)|EVP_SignInit(3)>,
-L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>,
-L<OpenSSL_add_all_algorithms(3)|OpenSSL_add_all_algorithms(3)>,
-L<engine(3)|engine(3)>
+L<EVP_DigestInit(3)>,
+L<EVP_EncryptInit(3)>,
+L<EVP_OpenInit(3)>,
+L<EVP_SealInit(3)>,
+L<EVP_DigestSignInit(3)>,
+L<EVP_SignInit(3)>,
+L<EVP_VerifyInit(3)>,
+L<EVP_PKEY_new(3)>,
+L<EVP_PKEY_set1_RSA(3)>,
+L<EVP_PKEY_keygen(3)>,
+L<EVP_PKEY_print_private(3)>,
+L<EVP_PKEY_decrypt(3)>,
+L<EVP_PKEY_encrypt(3)>,
+L<EVP_PKEY_sign(3)>,
+L<EVP_PKEY_verify(3)>,
+L<EVP_PKEY_verify_recover(3)>,
+L<EVP_PKEY_derive(3)>,
+L<EVP_BytesToKey(3)>,
+L<engine(3)>
=cut
projects / openssl.git / blobdiff