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204 lines
8.0 KiB
Plaintext
204 lines
8.0 KiB
Plaintext
=pod
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=head1 NAME
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EVP_DigestVerifyInit_ex, EVP_DigestVerifyInit, EVP_DigestVerifyUpdate,
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EVP_DigestVerifyFinal, EVP_DigestVerify - EVP signature verification functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_DigestVerifyInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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const char *mdname, OSSL_LIB_CTX *libctx,
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const char *props, EVP_PKEY *pkey,
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const OSSL_PARAM params[]);
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int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
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int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
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int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig,
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size_t siglen);
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int EVP_DigestVerify(EVP_MD_CTX *ctx, const unsigned char *sig,
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size_t siglen, const unsigned char *tbs, size_t tbslen);
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=head1 DESCRIPTION
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The EVP signature routines are a high-level interface to digital signatures.
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Input data is digested first before the signature verification takes place.
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EVP_DigestVerifyInit_ex() sets up verification context B<ctx> to use a
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digest with the name B<mdname> and public key B<pkey>. The name of the digest to
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be used is passed to the provider of the signature algorithm in use. How that
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provider interprets the digest name is provider specific. The provider may
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implement that digest directly itself or it may (optionally) choose to fetch it
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(which could result in a digest from a different provider being selected). If
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the provider supports fetching the digest then it may use the B<props> argument
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for the properties to be used during the fetch. Finally, the passed parameters
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I<params>, if not NULL, are set on the context before returning.
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The I<pkey> algorithm is used to fetch a B<EVP_SIGNATURE> method implicitly, to
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be used for the actual signing. See L<provider(7)/Implicit fetch> for
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more information about implicit fetches.
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The OpenSSL default and legacy providers support fetching digests and can fetch
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those digests from any available provider. The OpenSSL FIPS provider also
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supports fetching digests but will only fetch digests that are themselves
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implemented inside the FIPS provider.
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B<ctx> must be created with EVP_MD_CTX_new() before calling this function. If
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B<pctx> is not NULL, the EVP_PKEY_CTX of the verification operation will be
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written to B<*pctx>: this can be used to set alternative verification options.
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Note that any existing value in B<*pctx> is overwritten. The EVP_PKEY_CTX value
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returned must not be freed directly by the application if B<ctx> is not assigned
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an EVP_PKEY_CTX value before being passed to EVP_DigestVerifyInit_ex()
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(which means the EVP_PKEY_CTX is created inside
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EVP_DigestVerifyInit_ex() and it will be freed automatically when the
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EVP_MD_CTX is freed). If the EVP_PKEY_CTX to be used is created by
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EVP_DigestVerifyInit_ex then it will use the B<OSSL_LIB_CTX> specified
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in I<libctx> and the property query string specified in I<props>.
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No B<EVP_PKEY_CTX> will be created by EVP_DigestVerifyInit_ex() if the
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passed B<ctx> has already been assigned one via L<EVP_MD_CTX_set_pkey_ctx(3)>.
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See also L<SM2(7)>.
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Not all digests can be used for all key types. The following combinations apply.
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=over 4
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=item DSA
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Supports SHA1, SHA224, SHA256, SHA384 and SHA512
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=item ECDSA
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Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3
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=item RSA with no padding
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Supports no digests (the digest B<type> must be NULL)
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=item RSA with X931 padding
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Supports SHA1, SHA256, SHA384 and SHA512
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=item All other RSA padding types
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Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2, MD4, MDC2,
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SHA3-224, SHA3-256, SHA3-384, SHA3-512
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=item Ed25519 and Ed448
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Support no digests (the digest B<type> must be NULL)
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=item HMAC
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Supports any digest
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=item CMAC, Poly1305 and Siphash
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Will ignore any digest provided.
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=back
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If RSA-PSS is used and restrictions apply then the digest must match.
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EVP_DigestVerifyInit() works in the same way as
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EVP_DigestVerifyInit_ex() except that the B<mdname> parameter will be
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inferred from the supplied digest B<type>, and B<props> will be NULL. Where
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supplied the ENGINE B<e> will be used for the signature verification and digest
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algorithm implementations. B<e> may be NULL.
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EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the
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verification context B<ctx>. This function can be called several times on the
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same B<ctx> to include additional data.
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EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in
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B<sig> of length B<siglen>.
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EVP_DigestVerify() verifies B<tbslen> bytes at B<tbs> against the signature
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in B<sig> of length B<siglen>.
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=head1 RETURN VALUES
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EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0
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for failure.
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EVP_DigestVerifyFinal() and EVP_DigestVerify() return 1 for success; any other
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value indicates failure. A return value of zero indicates that the signature
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did not verify successfully (that is, B<tbs> did not match the original data or
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the signature had an invalid form), while other values indicate a more serious
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error (and sometimes also indicate an invalid signature form).
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The error codes can be obtained from L<ERR_get_error(3)>.
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=head1 NOTES
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The B<EVP> interface to digital signatures should almost always be used in
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preference to the low-level interfaces. This is because the code then becomes
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transparent to the algorithm used and much more flexible.
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EVP_DigestVerify() is a one shot operation which verifies a single block of
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data in one function. For algorithms that support streaming it is equivalent
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to calling EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal(). For
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algorithms which do not support streaming (e.g. PureEdDSA) it is the only way
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to verify data.
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In previous versions of OpenSSL there was a link between message digest types
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and public key algorithms. This meant that "clone" digests such as EVP_dss1()
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needed to be used to sign using SHA1 and DSA. This is no longer necessary and
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the use of clone digest is now discouraged.
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For some key types and parameters the random number generator must be seeded.
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If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
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external circumstances (see L<RAND(7)>), the operation will fail.
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The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest
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context. This means that EVP_VerifyUpdate() and EVP_VerifyFinal() can
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be called later to digest and verify additional data. Applications may disable
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this behavior by setting the EVP_MD_CTX_FLAG_FINALISE context flag via
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L<EVP_MD_CTX_set_flags(3)>.
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Note that not all providers support continuation, in case the selected
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provider does not allow to duplicate contexts EVP_DigestVerifyFinal() will
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finalize the digest context and attempting to process additional data via
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EVP_DigestVerifyUpdate() will result in an error.
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EVP_DigestVerifyInit() and EVP_DigestVerifyInit_ex() functions can be called
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multiple times on a context and the parameters set by previous calls should be
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preserved if the I<pkey> parameter is NULL. The call then just resets the state
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of the I<ctx>.
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Ignoring failure returns of EVP_DigestVerifyInit() and EVP_DigestVerifyInit_ex()
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functions can lead to subsequent undefined behavior when calling
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EVP_DigestVerifyUpdate(), EVP_DigestVerifyFinal(), or EVP_DigestVerify().
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=head1 SEE ALSO
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L<EVP_DigestSignInit(3)>,
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L<EVP_DigestInit(3)>,
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L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
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L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
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L<SHA1(3)>, L<openssl-dgst(1)>,
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L<RAND(7)>
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=head1 HISTORY
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EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal()
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were added in OpenSSL 1.0.0.
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EVP_DigestVerifyInit_ex() was added in OpenSSL 3.0.
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EVP_DigestVerifyUpdate() was converted from a macro to a function in OpenSSL
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3.0.
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=head1 COPYRIGHT
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Copyright 2006-2023 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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