EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal, EVP_DigestVerify - EVP signature verification functions
#include <openssl/evp.h> int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt); int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig, size_t siglen); int EVP_DigestVerify(EVP_MD_CTX *ctx, const unsigned char *sigret, size_t siglen, const unsigned char *tbs, size_t tbslen);
The EVP signature routines are a high level interface to digital signatures.
EVP_DigestVerifyInit() sets up verification context ctx to use digest type from ENGINE e and public key pkey. ctx must be created with EVP_MD_CTX_new() before calling this function. If pctx is not NULL, the EVP_PKEY_CTX of the verification operation will be written to *pctx: this can be used to set alternative verification options. Note that any existing value in *pctx is overwritten. The EVP_PKEY_CTX value returned must not be freed directly by the application if ctx is not assigned an EVP_PKEY_CTX value before being passed to EVP_DigestVerifyInit() (which means the EVP_PKEY_CTX is created inside EVP_DigestVerifyInit() and it will be freed automatically when the EVP_MD_CTX is freed).
EVP_DigestVerifyUpdate() 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. This function is currently implemented using a macro.
EVP_DigestVerifyFinal() verifies the data in ctx against the signature in sig of length siglen.
EVP_DigestVerify() verifies tbslen bytes at tbs against the signature in sig of length siglen.
EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0 for failure.
EVP_DigestVerifyFinal() and EVP_DigestVerify() return 1 for success; any other value indicates failure. A return value of zero indicates that the signature did not verify successfully (that is, tbs 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).
The error codes can be obtained from 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.
EVP_DigestVerify() is a one shot operation which verifies a single block of data in one function. For algorithms that support streaming it is equivalent to calling EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal(). For algorithms which do not support streaming (e.g. PureEdDSA) it is the only way to verify data.
In previous versions of OpenSSL there was a link between message digest types and public key algorithms. This meant that "clone" digests such as EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no longer necessary and the use of clone digest is now discouraged.
For some key types and parameters the random number generator must be seeded. If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to external circumstances (see RAND(7)), the operation will fail.
The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest context. This means that 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.
EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() were added in OpenSSL 1.0.0.
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