/usr/man/cat.3/EVP_DigestVerifyInit.3

EVP_DigestVerifyInit(3)      OpenSSL      EVP_DigestVerifyInit(3)

NAME

     EVP_DigestVerifyInit, EVP_DigestVerifyUpdate,
     EVP_DigestVerifyFinal - EVP signature verification functions

SYNOPSIS

      #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);

DESCRIPTION

     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 impl and public key pkey. ctx
     must be initialized with EVP_MD_CTX_init() 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
     (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.

RETURN VALUES

     EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1
     for success and 0 or a negative value for failure. In
     particular a return value of -2 indicates the operation is
     not supported by the public key algorithm.

     EVP_DigestVerifyFinal() returns 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).

1.0.2t               Last change: 2019-09-10                    1

EVP_DigestVerifyInit(3)      OpenSSL      EVP_DigestVerifyInit(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.

     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 or 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_cleanup() or a memory leak will occur.

SEE ALSO

     EVP_DigestSignInit(3), EVP_DigestInit(3), err(3), evp(3),
     hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)

HISTORY

     EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and
     EVP_DigestVerifyFinal() were first added to OpenSSL 1.0.0.

1.0.2t               Last change: 2019-09-10                    2

See also EVP_DigestVerifyFinal(3)
See also EVP_DigestVerifyUpdate(3)