.\" $OpenBSD: EVP_DigestVerifyInit.3,v 1.6 2018/05/13 14:00:22 schwarze Exp $ .\" OpenSSL fb552ac6 Sep 30 23:43:01 2009 +0000 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2006, 2009, 2014, 2015, 2016 The OpenSSL Project. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: May 13 2018 $ .Dt EVP_DIGESTVERIFYINIT 3 .Os .Sh NAME .Nm EVP_DigestVerifyInit , .Nm EVP_DigestVerifyUpdate , .Nm EVP_DigestVerifyFinal .Nd EVP signature verification functions .Sh SYNOPSIS .In openssl/evp.h .Ft int .Fo EVP_DigestVerifyInit .Fa "EVP_MD_CTX *ctx" .Fa "EVP_PKEY_CTX **pctx" .Fa "const EVP_MD *type" .Fa "ENGINE *e" .Fa "EVP_PKEY *pkey" .Fc .Ft int .Fo EVP_DigestVerifyUpdate .Fa "EVP_MD_CTX *ctx" .Fa "const void *d" .Fa "size_t cnt" .Fc .Ft int .Fo EVP_DigestVerifyFinal .Fa "EVP_MD_CTX *ctx" .Fa "const unsigned char *sig" .Fa "size_t siglen" .Fc .Sh DESCRIPTION The EVP signature routines are a high level interface to digital signatures. .Pp .Fn EVP_DigestVerifyInit sets up verification context .Fa ctx to use digest .Fa type from .Vt ENGINE .Fa e and public key .Fa pkey . .Fa ctx must be initialized with .Xr EVP_MD_CTX_init 3 before calling this function. If .Fa pctx is not .Dv NULL , the .Vt EVP_PKEY_CTX of the verification operation will be written to .Pf * Fa pctx : this can be used to set alternative verification options. .Pp .Fn EVP_DigestVerifyUpdate hashes .Fa cnt bytes of data at .Fa d into the verification context .Fa ctx . This function can be called several times on the same .Fa ctx to include additional data. This function is currently implemented using a macro. .Pp .Fn EVP_DigestVerifyFinal verifies the data in .Fa ctx against the signature in .Fa sig of length .Fa siglen . .Pp The EVP interface to digital signatures should almost always be used in preference to the low level interfaces. This is because the code then becomes transparent to the algorithm used and much more flexible. .Pp In previous versions of OpenSSL, there was a link between message digest types and public key algorithms. This meant that "clone" digests such as .Xr EVP_dss1 3 needed to be used to sign using SHA1 and DSA. This is no longer necessary and the use of clone digest is now discouraged. .Pp The call to .Fn EVP_DigestVerifyFinal internally finalizes a copy of the digest context. This means that .Xr EVP_VerifyUpdate 3 and .Xr EVP_VerifyFinal 3 can be called later to digest and verify additional data. .Pp Since only a copy of the digest context is ever finalized, the context must be cleaned up after use by calling .Xr EVP_MD_CTX_cleanup 3 or a memory leak will occur. .Sh RETURN VALUES .Fn EVP_DigestVerifyInit and .Fn EVP_DigestVerifyUpdate return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm. .Pp .Fn EVP_DigestVerifyFinal returns 1 for success; any other value indicates failure. A return value of 0 indicates that the signature did not verify successfully (that is, the signature did not match the original data or the signature had an invalid form), while other values indicate a more serious error (and sometimes also indicate an invalid signature form). .Pp The error codes can be obtained from .Xr ERR_get_error 3 . .Sh SEE ALSO .Xr ERR 3 , .Xr evp 3 , .Xr EVP_DigestInit 3 , .Xr EVP_DigestSignInit 3 , .Xr EVP_PKEY_meth_set_verifyctx 3 .Sh HISTORY .Fn EVP_DigestVerifyInit , .Fn EVP_DigestVerifyUpdate , and .Fn EVP_DigestVerifyFinal first appeared in OpenSSL 1.0.0 and have been available since .Ox 4.9 .