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Diffstat (limited to 'openssl/doc/crypto/EVP_PKEY_verify_recover.pod')
-rw-r--r-- | openssl/doc/crypto/EVP_PKEY_verify_recover.pod | 103 |
1 files changed, 103 insertions, 0 deletions
diff --git a/openssl/doc/crypto/EVP_PKEY_verify_recover.pod b/openssl/doc/crypto/EVP_PKEY_verify_recover.pod new file mode 100644 index 0000000..23a28a9 --- /dev/null +++ b/openssl/doc/crypto/EVP_PKEY_verify_recover.pod @@ -0,0 +1,103 @@ +=pod + +=head1 NAME + +EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover - recover signature using a public key algorithm + +=head1 SYNOPSIS + + #include <openssl/evp.h> + + int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx); + int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx, + unsigned char *rout, size_t *routlen, + const unsigned char *sig, size_t siglen); + +=head1 DESCRIPTION + +The EVP_PKEY_verify_recover_init() function initializes a public key algorithm +context using key B<pkey> for a verify recover operation. + +The EVP_PKEY_verify_recover() function recovers signed data +using B<ctx>. The signature is specified using the B<sig> and +B<siglen> parameters. If B<rout> is B<NULL> then the maximum size of the output +buffer is written to the B<routlen> parameter. If B<rout> is not B<NULL> then +before the call the B<routlen> parameter should contain the length of the +B<rout> buffer, if the call is successful recovered data is written to +B<rout> and the amount of data written to B<routlen>. + +=head1 NOTES + +Normally an application is only interested in whether a signature verification +operation is successful in those cases the EVP_verify() function should be +used. + +Sometimes however it is useful to obtain the data originally signed using a +signing operation. Only certain public key algorithms can recover a signature +in this way (for example RSA in PKCS padding mode). + +After the call to EVP_PKEY_verify_recover_init() algorithm specific control +operations can be performed to set any appropriate parameters for the +operation. + +The function EVP_PKEY_verify_recover() can be called more than once on the same +context if several operations are performed using the same parameters. + +=head1 RETURN VALUES + +EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() 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. + +=head1 EXAMPLE + +Recover digest originally signed using PKCS#1 and SHA256 digest: + + #include <openssl/evp.h> + #include <openssl/rsa.h> + + EVP_PKEY_CTX *ctx; + unsigned char *rout, *sig; + size_t routlen, siglen; + EVP_PKEY *verify_key; + /* NB: assumes verify_key, sig and siglen are already set up + * and that verify_key is an RSA public key + */ + ctx = EVP_PKEY_CTX_new(verify_key); + if (!ctx) + /* Error occurred */ + if (EVP_PKEY_verify_recover_init(ctx) <= 0) + /* Error */ + if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) + /* Error */ + if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) + /* Error */ + + /* Determine buffer length */ + if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0) + /* Error */ + + rout = OPENSSL_malloc(routlen); + + if (!rout) + /* malloc failure */ + + if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0) + /* Error */ + + /* Recovered data is routlen bytes written to buffer rout */ + +=head1 SEE ALSO + +L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>, +L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>, +L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>, +L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>, +L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>, +L<EVP_PKEY_derive(3)|EVP_PKEY_derive(3)> + +=head1 HISTORY + +These functions were first added to OpenSSL 1.0.0. + +=cut |