EVP_VerifyInit

- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- NOTES
- BUGS
- SEE ALSO
- COPYRIGHT

# NAME

EVP_VerifyInit_ex, EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal - EVP signature verification functions

# SYNOPSIS

     #include <openssl/evp.h>

     int EVP_VerifyInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
     int EVP_VerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
     int EVP_VerifyFinal(EVP_MD_CTX *ctx, unsigned char *sigbuf, unsigned int siglen,
                         EVP_PKEY *pkey);

     int EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);

# DESCRIPTION

The EVP signature verification routines are a high-level interface to digital signatures.

`EVP_VerifyInit_ex()` sets up verification context ctx to use digest type from ENGINE impl. ctx must be created by calling `EVP_MD_CTX_new()` before calling this function.

`EVP_VerifyUpdate()` hashes cnt bytes of data at d into the verification context ctx. This function can be called several times on the same ctx to include additional data.

`EVP_VerifyFinal()` verifies the data in ctx using the public key pkey and against the siglen bytes at sigbuf.

`EVP_VerifyInit()` initializes verification context ctx to use the default implementation of digest type.

# RETURN VALUES

`EVP_VerifyInit_ex()` and `EVP_VerifyUpdate()` return 1 for success and 0 for failure.

`EVP_VerifyFinal()` returns 1 for a correct signature, 0 for failure and -1 if some other error occurred.

The error codes can be obtained by ERR_get_error(3).

# NOTES

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.

The call to `EVP_VerifyFinal()` internally finalizes a copy of the digest context. This means that calls to `EVP_VerifyUpdate()` and `EVP_VerifyFinal()` can be called later to digest and verify additional data.

Since only a copy of the digest context is ever finalized the context must be cleaned up after use by calling `EVP_MD_CTX_free()` or a memory leak will occur.

# BUGS

Older versions of this documentation wrongly stated that calls to `EVP_VerifyUpdate()` could not be made after calling `EVP_VerifyFinal()`.

Since the public key is passed in the call to `EVP_SignFinal()` 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 `EVP_SignUpdate()`.

It is not possible to change the signing parameters using these function.

The previous two bugs are fixed in the newer EVP_DigestVerify*() function.

# SEE ALSO

evp(7), EVP_SignInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3), MD5(3), MDC2(3), RIPEMD160(3), SHA1(3), dgst(1)

# COPYRIGHT

Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.