.\" $OpenBSD: EVP_VerifyInit.3,v 1.4 2016/11/26 20:55:26 schwarze Exp $ .\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2000, 2001, 2006, 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: November 26 2016 $ .Dt EVP_VERIFYINIT 3 .Os .Sh NAME .Nm EVP_VerifyInit_ex , .Nm EVP_VerifyUpdate , .Nm EVP_VerifyFinal , .Nm EVP_VerifyInit .Nd EVP signature verification functions .Sh SYNOPSIS .In openssl/evp.h .Ft int .Fo EVP_VerifyInit_ex .Fa "EVP_MD_CTX *ctx" .Fa "const EVP_MD *type" .Fa "ENGINE *impl" .Fc .Ft int .Fo EVP_VerifyUpdate .Fa "EVP_MD_CTX *ctx" .Fa "const void *d" .Fa "unsigned int cnt" .Fc .Ft int .Fo EVP_VerifyFinal .Fa "EVP_MD_CTX *ctx" .Fa "unsigned char *sigbuf" .Fa "unsigned int siglen" .Fa "EVP_PKEY *pkey" .Fc .Ft int .Fo EVP_VerifyInit .Fa "EVP_MD_CTX *ctx" .Fa "const EVP_MD *type" .Fc .Sh DESCRIPTION The EVP signature verification routines are a high level interface to digital signatures. .Pp .Fn EVP_VerifyInit_ex sets up a verification context .Fa ctx to use the digest .Fa type from .Vt ENGINE .Fa impl . .Fa ctx must be initialized by calling .Xr EVP_MD_CTX_init 3 before calling this function. .Pp .Fn EVP_VerifyUpdate 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. .Pp .Fn EVP_VerifyFinal verifies the data in .Fa ctx using the public key .Fa pkey and against the .Fa siglen bytes at .Fa sigbuf . .Pp .Fn EVP_VerifyInit initializes a verification context .Fa ctx to use the default implementation of digest .Fa type . .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 Due to the link between message digests and public key algorithms, the correct digest algorithm must be used with the correct public key type. A list of algorithms and associated public key algorithms appears in .Xr EVP_DigestInit 3 . .Pp The call to .Fn EVP_VerifyFinal internally finalizes a copy of the digest context. This means that calls to .Fn EVP_VerifyUpdate and .Fn EVP_VerifyFinal 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_VerifyInit_ex and .Fn EVP_VerifyUpdate return 1 for success and 0 for failure. .Pp .Fn EVP_VerifyFinal returns 1 for a correct signature, 0 for failure, and -1 if some other error occurred. .Pp The error codes can be obtained by .Xr ERR_get_error 3 . .Sh SEE ALSO .Xr ERR 3 , .Xr evp 3 , .Xr EVP_DigestInit 3 , .Xr EVP_SignInit 3 .Sh HISTORY .Fn EVP_VerifyInit , .Fn EVP_VerifyUpdate , and .Fn EVP_VerifyFinal are available in all versions of SSLeay and OpenSSL. .Pp .Fn EVP_VerifyInit_ex was added in OpenSSL 0.9.7. .Sh BUGS Older versions of this documentation wrongly stated that calls to .Fn EVP_VerifyUpdate could not be made after calling .Fn EVP_VerifyFinal . .Pp Since the public key is passed in the call to .Xr EVP_SignFinal 3 , any error relating to the private key (for example an unsuitable key and digest combination) will not be indicated until after potentially large amounts of data have been passed through .Xr EVP_SignUpdate 3 . .Pp It is not possible to change the signing parameters using these functions. .Pp The previous two bugs are fixed in the newer functions of the .Xr EVP_DigestVerifyInit 3 family.