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100 lines
4.2 KiB
Plaintext
100 lines
4.2 KiB
Plaintext
=pod
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=head1 NAME
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X509_build_chain,
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X509_verify_cert,
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X509_STORE_CTX_verify - build and verify X509 certificate chain
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=head1 SYNOPSIS
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#include <openssl/x509_vfy.h>
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STACK_OF(X509) *X509_build_chain(X509 *target, STACK_OF(X509) *certs,
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X509_STORE *store, int with_self_signed,
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OSSL_LIB_CTX *libctx, const char *propq);
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int X509_verify_cert(X509_STORE_CTX *ctx);
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int X509_STORE_CTX_verify(X509_STORE_CTX *ctx);
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=head1 DESCRIPTION
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X509_build_chain() builds a certificate chain starting from I<target>
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using the optional list of intermediate CA certificates I<certs>.
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If I<store> is NULL it builds the chain as far down as possible, ignoring errors.
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Else the chain must reach a trust anchor contained in I<store>.
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It internally uses a B<X509_STORE_CTX> structure associated with the library
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context I<libctx> and property query string I<propq>, both of which may be NULL.
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In case there is more than one possibility for the chain, only one is taken.
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On success it returns a pointer to a new stack of (up_ref'ed) certificates
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starting with I<target> and followed by all available intermediate certificates.
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A self-signed trust anchor is included only if I<target> is the trust anchor
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of I<with_self_signed> is 1.
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If a non-NULL stack is returned the caller is responsible for freeing it.
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The X509_verify_cert() function attempts to discover and validate a
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certificate chain based on parameters in I<ctx>.
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The verification context, of type B<X509_STORE_CTX>, can be constructed
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using L<X509_STORE_CTX_new(3)> and L<X509_STORE_CTX_init(3)>.
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It usually includes a target certificate to be verified,
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a set of certificates serving as trust anchors,
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a list of non-trusted certificates that may be helpful for chain construction,
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flags such as X509_V_FLAG_X509_STRICT, and various other optional components
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such as a callback function that allows customizing the verification outcome.
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A complete description of the certificate verification process is contained in
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the L<openssl-verification-options(1)> manual page.
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Applications rarely call this function directly but it is used by
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OpenSSL internally for certificate validation, in both the S/MIME and
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SSL/TLS code.
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A negative return value from X509_verify_cert() can occur if it is invoked
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incorrectly, such as with no certificate set in I<ctx>, or when it is called
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twice in succession without reinitialising I<ctx> for the second call.
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A negative return value can also happen due to internal resource problems
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or because an internal inconsistency has been detected.
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Applications must interpret any return value <= 0 as an error.
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The X509_STORE_CTX_verify() behaves like X509_verify_cert() except that its
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target certificate is the first element of the list of untrusted certificates
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in I<ctx> unless a target certificate is set explicitly.
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=head1 RETURN VALUES
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X509_build_chain() returns NULL on error, else a stack of certificates.
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Both X509_verify_cert() and X509_STORE_CTX_verify()
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return 1 if a complete chain can be built and validated,
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otherwise they return 0, and in exceptional circumstances (such as malloc
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failure and internal errors) they can also return a negative code.
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If a complete chain can be built and validated both functions return 1.
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If the certificate must be rejected on the basis of the data available
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or any required certificate status data is not available they return 0.
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If no definite answer possible they usually return a negative code.
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On error or failure additional error information can be obtained by
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examining I<ctx> using, for example, L<X509_STORE_CTX_get_error(3)>. Even if
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verification indicated success, the stored error code may be different from
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X509_V_OK, likely because a verification callback function has waived the error.
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=head1 SEE ALSO
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L<X509_STORE_CTX_new(3)>, L<X509_STORE_CTX_init(3)>,
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L<X509_STORE_CTX_get_error(3)>
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=head1 HISTORY
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X509_build_chain() and X509_STORE_CTX_verify() were added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2009-2022 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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