CMS_verify.pod 4.7 KB

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  1. =pod
  2. =head1 NAME
  3. CMS_verify - verify a CMS SignedData structure
  4. =head1 SYNOPSIS
  5. #include <openssl/cms.h>
  6. int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, unsigned int flags);
  7. STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
  8. =head1 DESCRIPTION
  9. CMS_verify() verifies a CMS SignedData structure. B<cms> is the CMS_ContentInfo
  10. structure to verify. B<certs> is a set of certificates in which to search for
  11. the signing certificate(s). B<store> is a trusted certificate store used for
  12. chain verification. B<indata> is the detached content if the content is not
  13. present in B<cms>. The content is written to B<out> if it is not NULL.
  14. B<flags> is an optional set of flags, which can be used to modify the verify
  15. operation.
  16. CMS_get0_signers() retrieves the signing certificate(s) from B<cms>, it must
  17. be called after a successful CMS_verify() operation.
  18. =head1 VERIFY PROCESS
  19. Normally the verify process proceeds as follows.
  20. Initially some sanity checks are performed on B<cms>. The type of B<cms> must
  21. be SignedData. There must be at least one signature on the data and if
  22. the content is detached B<indata> cannot be B<NULL>.
  23. An attempt is made to locate all the signing certificate(s), first looking in
  24. the B<certs> parameter (if it is not NULL) and then looking in any
  25. certificates contained in the B<cms> structure itself. If any signing
  26. certificate cannot be located the operation fails.
  27. Each signing certificate is chain verified using the B<smimesign> purpose and
  28. the supplied trusted certificate store. Any internal certificates in the message
  29. are used as untrusted CAs. If CRL checking is enabled in B<store> any internal
  30. CRLs are used in addition to attempting to look them up in B<store>. If any
  31. chain verify fails an error code is returned.
  32. Finally the signed content is read (and written to B<out> is it is not NULL)
  33. and the signature's checked.
  34. If all signature's verify correctly then the function is successful.
  35. Any of the following flags (ored together) can be passed in the B<flags>
  36. parameter to change the default verify behaviour.
  37. If B<CMS_NOINTERN> is set the certificates in the message itself are not
  38. searched when locating the signing certificate(s). This means that all the
  39. signing certificates must be in the B<certs> parameter.
  40. If B<CMS_NOCRL> is set and CRL checking is enabled in B<store> then any
  41. CRLs in the message itself are ignored.
  42. If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted
  43. from the content. If the content is not of type B<text/plain> then an error is
  44. returned.
  45. If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not
  46. verified.
  47. If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not
  48. verified.
  49. If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked.
  50. =head1 NOTES
  51. One application of B<CMS_NOINTERN> is to only accept messages signed by
  52. a small number of certificates. The acceptable certificates would be passed
  53. in the B<certs> parameter. In this case if the signer is not one of the
  54. certificates supplied in B<certs> then the verify will fail because the
  55. signer cannot be found.
  56. In some cases the standard techniques for looking up and validating
  57. certificates are not appropriate: for example an application may wish to
  58. lookup certificates in a database or perform customised verification. This
  59. can be achieved by setting and verifying the signers certificates manually
  60. using the signed data utility functions.
  61. Care should be taken when modifying the default verify behaviour, for example
  62. setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification
  63. and any modified content will be considered valid. This combination is however
  64. useful if one merely wishes to write the content to B<out> and its validity
  65. is not considered important.
  66. Chain verification should arguably be performed using the signing time rather
  67. than the current time. However since the signing time is supplied by the
  68. signer it cannot be trusted without additional evidence (such as a trusted
  69. timestamp).
  70. =head1 RETURN VALUES
  71. CMS_verify() returns 1 for a successful verification and zero if an error
  72. occurred.
  73. CMS_get0_signers() returns all signers or NULL if an error occurred.
  74. The error can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>
  75. =head1 BUGS
  76. The trusted certificate store is not searched for the signing certificate,
  77. this is primarily due to the inadequacies of the current B<X509_STORE>
  78. functionality.
  79. The lack of single pass processing means that the signed content must all
  80. be held in memory if it is not detached.
  81. =head1 SEE ALSO
  82. L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_sign(3)|CMS_sign(3)>
  83. =head1 HISTORY
  84. CMS_verify() was added to OpenSSL 0.9.8
  85. =cut