EVP_VERIFYINIT(3) | Library Functions Manual | EVP_VERIFYINIT(3)

# NAME

`EVP_VerifyInit_ex`, `EVP_VerifyUpdate`, `EVP_VerifyFinal`, `EVP_VerifyInit` — EVP signature verification functions

# SYNOPSIS

library “libcrypto”
`#include <openssl/evp.h>`

int
`EVP_VerifyInit_ex`(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *engine);

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 the verification context ctx to use the digest type. Before calling this function, obtain ctx from EVP_MD_CTX_new(3) or call EVP_MD_CTX_reset(3) on it. The engine argument is always ignored and passing `NULL` is recommended.

`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 a verification context ctx to use the default implementation of digest type.

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(3), or a memory leak will occur.

`EVP_VerifyInit_ex`(), `EVP_VerifyUpdate`(), and `EVP_VerifyInit`() are implemented as macros.

# 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).

# SEE ALSO

evp(3), EVP_DigestInit(3), EVP_SignInit(3)

# HISTORY

`EVP_VerifyInit`(), `EVP_VerifyUpdate`(), and `EVP_VerifyFinal`() first appeared in SSLeay 0.5.1 and have been available since OpenBSD 2.4.

`EVP_VerifyInit_ex`() first appeared in OpenSSL 0.9.7 and has been available since OpenBSD 3.2.

# 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(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 EVP_SignUpdate(3).

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

The previous two bugs are fixed in the newer functions of the EVP_DigestVerifyInit(3) family.

June 8, 2025 | Debian