.\"	$OpenBSD: evp.3,v 1.2 2016/11/06 15:52:50 jmc Exp $
.\"
.Dd $Mdocdate: November 6 2016 $
.Dt EVP 3
.Os
.Sh NAME
.Nm evp
.Nd high-level cryptographic functions
.Sh SYNOPSIS
.In openssl/evp.h
.Sh DESCRIPTION
The EVP library provides a high-level interface to cryptographic
functions.
.Pp
.Xr EVP_SealInit 3
and
.Xr EVP_OpenInit 3
provide public key encryption and decryption to implement digital
"envelopes".
.Pp
The
.Xr EVP_DigestSignInit 3
and
.Xr EVP_DigestVerifyInit 3
functions implement digital signatures and Message Authentication Codes
(MACs).
Also see the older
.Xr EVP_SignInit 3
and
.Xr EVP_VerifyInit 3
functions.
.Pp
Symmetric encryption is available with the
.Xr EVP_EncryptInit 3
functions.
The
.Xr EVP_DigestInit 3
functions provide message digests.
.Pp
Authenticated encryption with additional data (AEAD) is available with
the
.Xr EVP_AEAD_CTX_init 3
functions.
.Pp
The
.Fn EVP_PKEY_*
functions provide a high level interface to asymmetric algorithms.
To create a new
.Vt EVP_PKEY ,
see
.Xr EVP_PKEY_new 3 .
.Vt EVP_PKEY Ns s
can be associated with a private key of a particular algorithm
by using the functions described in the
.Xr EVP_PKEY_set1_RSA 3
page, or new keys can be generated using
.Xr EVP_PKEY_keygen 3 .
.Vt EVP_PKEY Ns s
can be compared using
.Xr EVP_PKEY_cmp 3
or printed using
.Xr EVP_PKEY_print_private 3 .
.Pp
The
.Fn EVP_PKEY_*
functions support the full range of asymmetric algorithm operations:
.Bl -bullet
.It
For key agreement, see
.Xr EVP_PKEY_derive 3 .
.It
For signing and verifying, see
.Xr EVP_PKEY_sign 3 ,
.Xr EVP_PKEY_verify 3 ,
and
.Xr 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
.Xr EVP_DigestSignInit 3
functions for this purpose.
.It
For encryption and decryption see
.Xr EVP_PKEY_encrypt 3
and
.Xr 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
.Xr EVP_SealInit 3
and
.Xr EVP_OpenInit 3
functions.
.El
.Pp
The
.Xr 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 typically not use this (preferring, for
example, PBKDF2 from PCKS#5).
.Pp
Algorithms are loaded with
.Xr OpenSSL_add_all_algorithms 3 .
.Pp
All the symmetric algorithms (ciphers), digests and asymmetric
algorithms (public key algorithms) can be replaced by
.Xr engine 3
modules providing alternative implementations.
If
.Vt ENGINE
implementations of ciphers or digests are registered as defaults,
then the various EVP functions will automatically use those
implementations in preference to built in software implementations.
For more information, consult the
.Xr engine 3
manual page.
.Pp
Although low level algorithm specific functions exist for many
algorithms, their use is discouraged.
They cannot be used with an
.Vt ENGINE ,
and
.Vt ENGINE
versions of new algorithms cannot be accessed using the low level
functions.
Using them also makes code harder to adapt to new algorithms, some
options are not cleanly supported at the low level, and some
operations are more efficient using the high level interfaces.
.Sh SEE ALSO
.Xr engine 3 ,
.Xr EVP_AEAD_CTX_init 3 ,
.Xr EVP_BytesToKey 3 ,
.Xr EVP_DigestInit 3 ,
.Xr EVP_DigestSignInit 3 ,
.Xr EVP_EncryptInit 3 ,
.Xr EVP_OpenInit 3 ,
.Xr EVP_PKEY_decrypt 3 ,
.Xr EVP_PKEY_derive 3 ,
.Xr EVP_PKEY_encrypt 3 ,
.Xr EVP_PKEY_keygen 3 ,
.Xr EVP_PKEY_new 3 ,
.Xr EVP_PKEY_print_private 3 ,
.Xr EVP_PKEY_set1_RSA 3 ,
.Xr EVP_PKEY_sign 3 ,
.Xr EVP_PKEY_verify 3 ,
.Xr EVP_PKEY_verify_recover 3 ,
.Xr EVP_SealInit 3 ,
.Xr EVP_SignInit 3 ,
.Xr EVP_VerifyInit 3 ,
.Xr OpenSSL_add_all_algorithms 3