CMS_verify.pod 7.1 KB

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  1. =pod
  2. =head1 NAME
  3. CMS_verify, CMS_SignedData_verify,
  4. CMS_get0_signers - verify a CMS SignedData structure
  5. =head1 SYNOPSIS
  6. #include <openssl/cms.h>
  7. int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store,
  8. BIO *detached_data, BIO *out, unsigned int flags);
  9. BIO *CMS_SignedData_verify(CMS_SignedData *sd, BIO *detached_data,
  10. STACK_OF(X509) *scerts, X509_STORE *store,
  11. STACK_OF(X509) *extra, STACK_OF(X509_CRL) *crls,
  12. unsigned int flags,
  13. OSSL_LIB_CTX *libctx, const char *propq);
  14. STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
  15. =head1 DESCRIPTION
  16. CMS_verify() is very similar to L<PKCS7_verify(3)>. It verifies a
  17. B<CMS SignedData> structure contained in a structure of type B<CMS_ContentInfo>.
  18. I<cms> points to the B<CMS_ContentInfo> structure to verify.
  19. The optional I<certs> parameter refers to a set of certificates
  20. in which to search for signing certificates.
  21. I<cms> may contain extra untrusted CA certificates that may be used for
  22. chain building as well as CRLs that may be used for certificate validation.
  23. I<store> may be NULL or point to
  24. the trusted certificate store to use for chain verification.
  25. I<detached_data> refers to the signed data if the content is detached from I<cms>.
  26. Otherwise I<detached_data> should be NULL and the signed data must be in I<cms>.
  27. The content is written to the BIO I<out> unless it is NULL.
  28. I<flags> is an optional set of flags, which can be used to modify the operation.
  29. CMS_SignedData_verify() is like CMS_verify() except that
  30. it operates on B<CMS SignedData> input in the I<sd> argument,
  31. it has some additional parameters described next,
  32. and on success it returns the verified content as a memory BIO.
  33. The optional I<extra> parameter may be used to provide untrusted CA
  34. certificates that may be helpful for chain building in certificate validation.
  35. This list of certificates must not contain duplicates.
  36. The optional I<crls> parameter may be used to provide extra CRLs.
  37. Also the list of CRLs must not contain duplicates.
  38. The optional parameters library context I<libctx> and property query I<propq>
  39. are used when retrieving algorithms from providers.
  40. CMS_get0_signers() retrieves the signing certificate(s) from I<cms>; it may only
  41. be called after a successful CMS_verify() or CMS_SignedData_verify() operation.
  42. =head1 VERIFY PROCESS
  43. Normally the verify process proceeds as follows.
  44. Initially some sanity checks are performed on I<cms>. The type of I<cms> must
  45. be SignedData. There must be at least one signature on the data and if
  46. the content is detached I<detached_data> cannot be NULL.
  47. An attempt is made to locate all the signing certificate(s), first looking in
  48. the I<certs> parameter (if it is not NULL) and then looking in any
  49. certificates contained in the I<cms> structure unless B<CMS_NOINTERN> is set.
  50. If any signing certificate cannot be located the operation fails.
  51. Each signing certificate is chain verified using the I<smimesign> purpose and
  52. using the trusted certificate store I<store> if supplied.
  53. Any internal certificates in the message, which may have been added using
  54. L<CMS_add1_cert(3)>, are used as untrusted CAs.
  55. If CRL checking is enabled in I<store> and B<CMS_NOCRL> is not set,
  56. any internal CRLs, which may have been added using L<CMS_add1_crl(3)>,
  57. are used in addition to attempting to look them up in I<store>.
  58. If I<store> is not NULL and any chain verify fails an error code is returned.
  59. Finally the signed content is read (and written to I<out> unless it is NULL)
  60. and the signature is checked.
  61. If all signatures verify correctly then the function is successful.
  62. Any of the following flags (ored together) can be passed in the I<flags>
  63. parameter to change the default verify behaviour.
  64. If B<CMS_NOINTERN> is set the certificates in the message itself are not
  65. searched when locating the signing certificate(s).
  66. This means that all the signing certificates must be in the I<certs> parameter.
  67. If B<CMS_NOCRL> is set and CRL checking is enabled in I<store> then any
  68. CRLs in the message itself and provided via the I<crls> parameter are ignored.
  69. If the B<CMS_TEXT> flag is set MIME headers for type C<text/plain> are deleted
  70. from the content. If the content is not of type C<text/plain> then an error is
  71. returned.
  72. If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not
  73. chain verified, unless B<CMS_CADES> flag is also set.
  74. If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not
  75. verified, unless CMS_CADES flag is also set.
  76. If B<CMS_CADES> is set, each signer certificate is checked against the
  77. ESS signingCertificate or ESS signingCertificateV2 extension
  78. that is required in the signed attributes of the signature.
  79. If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked.
  80. =head1 NOTES
  81. One application of B<CMS_NOINTERN> is to only accept messages signed by
  82. a small number of certificates. The acceptable certificates would be passed
  83. in the I<certs> parameter. In this case if the signer certificate is not one
  84. of the certificates supplied in I<certs> then the verify will fail because the
  85. signer cannot be found.
  86. In some cases the standard techniques for looking up and validating
  87. certificates are not appropriate: for example an application may wish to
  88. lookup certificates in a database or perform customised verification. This
  89. can be achieved by setting and verifying the signer certificates manually
  90. using the signed data utility functions.
  91. Care should be taken when modifying the default verify behaviour, for example
  92. setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification
  93. and any modified content will be considered valid. This combination is however
  94. useful if one merely wishes to write the content to I<out> and its validity
  95. is not considered important.
  96. Chain verification should arguably be performed using the signing time rather
  97. than the current time. However, since the signing time is supplied by the
  98. signer it cannot be trusted without additional evidence (such as a trusted
  99. timestamp).
  100. =head1 RETURN VALUES
  101. CMS_verify() returns 1 for a successful verification and 0 if an error occurred.
  102. CMS_SignedData_verify() returns a memory BIO containing the verified content,
  103. or NULL on error.
  104. CMS_get0_signers() returns all signers or NULL if an error occurred.
  105. The error can be obtained from L<ERR_get_error(3)>.
  106. =head1 BUGS
  107. The trusted certificate store is not searched for the signing certificate.
  108. This is primarily due to the inadequacies of the current B<X509_STORE>
  109. functionality.
  110. The lack of single pass processing means that the signed content must all
  111. be held in memory if it is not detached.
  112. =head1 SEE ALSO
  113. L<PKCS7_verify(3)>, L<CMS_add1_cert(3)>, L<CMS_add1_crl(3)>,
  114. L<OSSL_ESS_check_signing_certs(3)>,
  115. L<ERR_get_error(3)>, L<CMS_sign(3)>
  116. =head1 HISTORY
  117. CMS_SignedData_verify() was added in OpenSSL 3.2.
  118. =head1 COPYRIGHT
  119. Copyright 2008-2023 The OpenSSL Project Authors. All Rights Reserved.
  120. Licensed under the Apache License 2.0 (the "License"). You may not use
  121. this file except in compliance with the License. You can obtain a copy
  122. in the file LICENSE in the source distribution or at
  123. L<https://www.openssl.org/source/license.html>.
  124. =cut