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103 lines
3.2 KiB
103 lines
3.2 KiB
=pod |
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=head1 NAME |
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EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover - recover signature using a public key algorithm |
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=head1 SYNOPSIS |
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#include <openssl/evp.h> |
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int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx); |
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int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx, |
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unsigned char *rout, size_t *routlen, |
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const unsigned char *sig, size_t siglen); |
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=head1 DESCRIPTION |
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The EVP_PKEY_verify_recover_init() function initializes a public key algorithm |
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context using key B<pkey> for a verify recover operation. |
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The EVP_PKEY_verify_recover() function recovers signed data |
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using B<ctx>. The signature is specified using the B<sig> and |
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B<siglen> parameters. If B<rout> is B<NULL> then the maximum size of the output |
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buffer is written to the B<routlen> parameter. If B<rout> is not B<NULL> then |
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before the call the B<routlen> parameter should contain the length of the |
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B<rout> buffer, if the call is successful recovered data is written to |
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B<rout> and the amount of data written to B<routlen>. |
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=head1 NOTES |
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Normally an application is only interested in whether a signature verification |
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operation is successful in those cases the EVP_verify() function should be |
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used. |
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Sometimes however it is useful to obtain the data originally signed using a |
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signing operation. Only certain public key algorithms can recover a signature |
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in this way (for example RSA in PKCS padding mode). |
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After the call to EVP_PKEY_verify_recover_init() algorithm specific control |
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operations can be performed to set any appropriate parameters for the |
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operation. |
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The function EVP_PKEY_verify_recover() can be called more than once on the same |
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context if several operations are performed using the same parameters. |
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=head1 RETURN VALUES |
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EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success |
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and 0 or a negative value for failure. In particular a return value of -2 |
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indicates the operation is not supported by the public key algorithm. |
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=head1 EXAMPLE |
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Recover digest originally signed using PKCS#1 and SHA256 digest: |
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#include <openssl/evp.h> |
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#include <openssl/rsa.h> |
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EVP_PKEY_CTX *ctx; |
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unsigned char *rout, *sig; |
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size_t routlen, siglen; |
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EVP_PKEY *verify_key; |
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/* NB: assumes verify_key, sig and siglen are already set up |
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* and that verify_key is an RSA public key |
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*/ |
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ctx = EVP_PKEY_CTX_new(verify_key); |
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if (!ctx) |
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/* Error occurred */ |
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if (EVP_PKEY_verify_recover_init(ctx) <= 0) |
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/* Error */ |
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if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) |
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/* Error */ |
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if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) |
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/* Error */ |
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/* Determine buffer length */ |
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if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0) |
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/* Error */ |
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rout = OPENSSL_malloc(routlen); |
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if (!rout) |
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/* malloc failure */ |
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if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0) |
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/* Error */ |
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/* Recovered data is routlen bytes written to buffer rout */ |
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=head1 SEE ALSO |
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L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>, |
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L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>, |
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L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>, |
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L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>, |
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L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>, |
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L<EVP_PKEY_derive(3)|EVP_PKEY_derive(3)> |
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=head1 HISTORY |
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These functions were first added to OpenSSL 1.0.0. |
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=cut
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