EVP_VerifyInit_ex, EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal_ex, EVP_VerifyFinal - EVP signature verification functions
#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_ex(EVP_MD_CTX *ctx, const unsigned char *sigbuf, unsigned int siglen, EVP_PKEY *pkey, OSSL_LIB_CTX *libctx, const char *propq); 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);
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_ex() verifies the data in ctx using the public key pkey and siglen bytes in sigbuf. The library context libctx and property query propq are used when creating a context to use with the key pkey.
EVP_VerifyFinal() is similar to EVP_VerifyFinal_ex() but uses default values of NULL for the library context libctx and the property query propq.
EVP_VerifyInit() initializes verification context ctx to use the default implementation of digest type.
EVP_VerifyInit_ex() and EVP_VerifyUpdate() return 1 for success and 0 for failure.
EVP_VerifyFinal_ex() and EVP_VerifyFinal() return 1 for a correct signature, 0 for failure and a negative value if some other error occurred.
The error codes can be obtained by ERR_get_error(3).
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. Applications may disable this behavior by setting the EVP_MD_CTX_FLAG_FINALISE context flag via EVP_MD_CTX_set_flags(3).
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.
Note that not all providers support continuation, in case the selected provider does not allow to duplicate contexts EVP_VerifyFinal() will finalize the digest context and attempting to process additional data via EVP_VerifyUpdate() will result in an error.
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.
The function EVP_VerifyFinal_ex() was added in OpenSSL 3.0.
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