| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | X509_build_chain,
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| 6 | X509_verify_cert,
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| 7 | X509_STORE_CTX_verify - build and verify X509 certificate chain
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| 8 |
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| 9 | =head1 SYNOPSIS
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| 10 |
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| 11 | #include <openssl/x509_vfy.h>
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| 12 |
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| 13 | STACK_OF(X509) *X509_build_chain(X509 *target, STACK_OF(X509) *certs,
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| 14 | X509_STORE *store, int with_self_signed,
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| 15 | OSSL_LIB_CTX *libctx, const char *propq);
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| 16 | int X509_verify_cert(X509_STORE_CTX *ctx);
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| 17 | int X509_STORE_CTX_verify(X509_STORE_CTX *ctx);
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| 18 |
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| 19 | =head1 DESCRIPTION
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| 20 |
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| 21 | X509_build_chain() builds a certificate chain starting from I<target>
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| 22 | using the optional list of intermediate CA certificates I<certs>.
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| 23 | If I<store> is NULL it builds the chain as far down as possible, ignoring errors.
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| 24 | Else the chain must reach a trust anchor contained in I<store>.
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| 25 | It internally uses a B<X509_STORE_CTX> structure associated with the library
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| 26 | context I<libctx> and property query string I<propq>, both of which may be NULL.
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| 27 | In case there is more than one possibility for the chain, only one is taken.
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| 28 |
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| 29 | On success it returns a pointer to a new stack of (up_ref'ed) certificates
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| 30 | starting with I<target> and followed by all available intermediate certificates.
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| 31 | A self-signed trust anchor is included only if I<target> is the trust anchor
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| 32 | of I<with_self_signed> is 1.
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| 33 | If a non-NULL stack is returned the caller is responsible for freeing it.
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| 34 |
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| 35 | The X509_verify_cert() function attempts to discover and validate a
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| 36 | certificate chain based on parameters in I<ctx>.
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| 37 | The verification context, of type B<X509_STORE_CTX>, can be constructed
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| 38 | using L<X509_STORE_CTX_new(3)> and L<X509_STORE_CTX_init(3)>.
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| 39 | It usually includes a target certificate to be verified,
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| 40 | a set of certificates serving as trust anchors,
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| 41 | a list of non-trusted certificates that may be helpful for chain construction,
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| 42 | flags such as X509_V_FLAG_X509_STRICT, and various other optional components
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| 43 | such as a callback function that allows customizing the verification outcome.
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| 44 | A complete description of the certificate verification process is contained in
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| 45 | the L<openssl-verification-options(1)> manual page.
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| 46 |
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| 47 | Applications rarely call this function directly but it is used by
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| 48 | OpenSSL internally for certificate validation, in both the S/MIME and
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| 49 | SSL/TLS code.
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| 50 |
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| 51 | A negative return value from X509_verify_cert() can occur if it is invoked
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| 52 | incorrectly, such as with no certificate set in I<ctx>, or when it is called
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| 53 | twice in succession without reinitialising I<ctx> for the second call.
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| 54 | A negative return value can also happen due to internal resource problems
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| 55 | or because an internal inconsistency has been detected.
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| 56 | Applications must interpret any return value <= 0 as an error.
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| 57 |
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| 58 | The X509_STORE_CTX_verify() behaves like X509_verify_cert() except that its
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| 59 | target certificate is the first element of the list of untrusted certificates
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| 60 | in I<ctx> unless a target certificate is set explicitly.
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| 61 |
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| 62 | =head1 RETURN VALUES
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| 63 |
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| 64 | X509_build_chain() returns NULL on error, else a stack of certificates.
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| 65 |
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| 66 | Both X509_verify_cert() and X509_STORE_CTX_verify()
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| 67 | return 1 if a complete chain can be built and validated,
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| 68 | otherwise they return 0, and in exceptional circumstances (such as malloc
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| 69 | failure and internal errors) they can also return a negative code.
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| 70 |
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| 71 | If a complete chain can be built and validated both functions return 1.
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| 72 | If the certificate must be rejected on the basis of the data available
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| 73 | or any required certificate status data is not available they return 0.
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| 74 | If no definite answer possible they usually return a negative code.
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| 75 |
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| 76 | On error or failure additional error information can be obtained by
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| 77 | examining I<ctx> using, for example, L<X509_STORE_CTX_get_error(3)>. Even if
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| 78 | verification indicated success, the stored error code may be different from
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| 79 | X509_V_OK, likely because a verification callback function has waived the error.
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| 80 |
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| 81 | =head1 SEE ALSO
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| 82 |
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| 83 | L<X509_STORE_CTX_new(3)>, L<X509_STORE_CTX_init(3)>,
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| 84 | L<X509_STORE_CTX_get_error(3)>
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| 85 |
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| 86 | =head1 HISTORY
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| 87 |
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| 88 | X509_build_chain() and X509_STORE_CTX_verify() were added in OpenSSL 3.0.
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| 89 |
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| 90 | =head1 COPYRIGHT
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| 91 |
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| 92 | Copyright 2009-2022 The OpenSSL Project Authors. All Rights Reserved.
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| 93 |
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| 94 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 95 | this file except in compliance with the License. You can obtain a copy
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| 96 | in the file LICENSE in the source distribution or at
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| 97 | L<https://www.openssl.org/source/license.html>.
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| 98 |
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| 99 | =cut
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