| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | EVP_PKEY_sign_init, EVP_PKEY_sign_init_ex, EVP_PKEY_sign
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| 6 | - sign using a public key algorithm
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| 7 |
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| 8 | =head1 SYNOPSIS
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| 9 |
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| 10 | #include <openssl/evp.h>
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| 11 |
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| 12 | int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx);
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| 13 | int EVP_PKEY_sign_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
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| 14 | int EVP_PKEY_sign(EVP_PKEY_CTX *ctx,
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| 15 | unsigned char *sig, size_t *siglen,
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| 16 | const unsigned char *tbs, size_t tbslen);
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| 17 |
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| 18 | =head1 DESCRIPTION
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| 19 |
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| 20 | EVP_PKEY_sign_init() initializes a public key algorithm context I<ctx> for
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| 21 | signing using the algorithm given when the context was created
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| 22 | using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to
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| 23 | fetch a B<EVP_SIGNATURE> method implicitly, see L<provider(7)/Implicit fetch>
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| 24 | for more information about implicit fetches.
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| 25 |
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| 26 | EVP_PKEY_sign_init_ex() is the same as EVP_PKEY_sign_init() but additionally
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| 27 | sets the passed parameters I<params> on the context before returning.
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| 28 |
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| 29 | The EVP_PKEY_sign() function performs a public key signing operation
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| 30 | using I<ctx>. The data to be signed is specified using the I<tbs> and
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| 31 | I<tbslen> parameters. If I<sig> is NULL then the maximum size of the output
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| 32 | buffer is written to the I<siglen> parameter. If I<sig> is not NULL then
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| 33 | before the call the I<siglen> parameter should contain the length of the
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| 34 | I<sig> buffer, if the call is successful the signature is written to
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| 35 | I<sig> and the amount of data written to I<siglen>.
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| 36 |
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| 37 | =head1 NOTES
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| 38 |
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| 39 | EVP_PKEY_sign() does not hash the data to be signed, and therefore is
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| 40 | normally used to sign digests. For signing arbitrary messages, see the
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| 41 | L<EVP_DigestSignInit(3)> and
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| 42 | L<EVP_SignInit(3)> signing interfaces instead.
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| 43 |
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| 44 | After the call to EVP_PKEY_sign_init() algorithm specific control
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| 45 | operations can be performed to set any appropriate parameters for the
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| 46 | operation (see L<EVP_PKEY_CTX_ctrl(3)>).
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| 47 |
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| 48 | The function EVP_PKEY_sign() can be called more than once on the same
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| 49 | context if several operations are performed using the same parameters.
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| 50 |
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| 51 | =head1 RETURN VALUES
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| 52 |
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| 53 | EVP_PKEY_sign_init() and EVP_PKEY_sign() return 1 for success and 0
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| 54 | or a negative value for failure. In particular a return value of -2
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| 55 | indicates the operation is not supported by the public key algorithm.
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| 56 |
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| 57 | =head1 EXAMPLES
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| 58 |
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| 59 | Sign data using RSA with PKCS#1 padding and SHA256 digest:
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| 60 |
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| 61 | #include <openssl/evp.h>
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| 62 | #include <openssl/rsa.h>
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| 63 |
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| 64 | EVP_PKEY_CTX *ctx;
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| 65 | /* md is a SHA-256 digest in this example. */
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| 66 | unsigned char *md, *sig;
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| 67 | size_t mdlen = 32, siglen;
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| 68 | EVP_PKEY *signing_key;
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| 69 |
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| 70 | /*
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| 71 | * NB: assumes signing_key and md are set up before the next
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| 72 | * step. signing_key must be an RSA private key and md must
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| 73 | * point to the SHA-256 digest to be signed.
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| 74 | */
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| 75 | ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
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| 76 | if (!ctx)
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| 77 | /* Error occurred */
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| 78 | if (EVP_PKEY_sign_init(ctx) <= 0)
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| 79 | /* Error */
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| 80 | if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
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| 81 | /* Error */
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| 82 | if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
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| 83 | /* Error */
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| 84 |
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| 85 | /* Determine buffer length */
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| 86 | if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0)
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| 87 | /* Error */
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| 88 |
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| 89 | sig = OPENSSL_malloc(siglen);
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| 90 |
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| 91 | if (!sig)
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| 92 | /* malloc failure */
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| 93 |
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| 94 | if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0)
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| 95 | /* Error */
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| 96 |
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| 97 | /* Signature is siglen bytes written to buffer sig */
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| 98 |
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| 99 |
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| 100 | =head1 SEE ALSO
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| 101 |
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| 102 | L<EVP_PKEY_CTX_new(3)>,
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| 103 | L<EVP_PKEY_CTX_ctrl(3)>,
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| 104 | L<EVP_PKEY_encrypt(3)>,
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| 105 | L<EVP_PKEY_decrypt(3)>,
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| 106 | L<EVP_PKEY_verify(3)>,
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| 107 | L<EVP_PKEY_verify_recover(3)>,
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| 108 | L<EVP_PKEY_derive(3)>
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| 109 |
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| 110 | =head1 HISTORY
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| 111 |
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| 112 | The EVP_PKEY_sign_init() and EVP_PKEY_sign() functions were added in
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| 113 | OpenSSL 1.0.0.
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| 114 |
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| 115 | The EVP_PKEY_sign_init_ex() function was added in OpenSSL 3.0.
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| 116 |
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| 117 | =head1 COPYRIGHT
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| 118 |
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| 119 | Copyright 2006-2021 The OpenSSL Project Authors. All Rights Reserved.
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| 120 |
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| 121 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 122 | this file except in compliance with the License. You can obtain a copy
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| 123 | in the file LICENSE in the source distribution or at
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| 124 | L<https://www.openssl.org/source/license.html>.
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| 125 |
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| 126 | =cut
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