PKCS7_verify.pod 4.5 KB

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  1. =pod
  2. =head1 NAME
  3. PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure
  4. =head1 SYNOPSIS
  5. #include <openssl/pkcs7.h>
  6. int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, int flags);
  7. STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
  8. =head1 DESCRIPTION
  9. PKCS7_verify() verifies a PKCS#7 signedData structure. B<p7> is the PKCS7
  10. structure to verify. B<certs> is a set of certificates in which to search for
  11. the signer's certificate. B<store> is a trusted certficate store (used for
  12. chain verification). B<indata> is the signed data if the content is not
  13. present in B<p7> (that is it is detached). The content is written to B<out>
  14. if it is not NULL.
  15. B<flags> is an optional set of flags, which can be used to modify the verify
  16. operation.
  17. PKCS7_get0_signers() retrieves the signer's certificates from B<p7>, it does
  18. B<not> check their validity or whether any signatures are valid. The B<certs>
  19. and B<flags> parameters have the same meanings as in PKCS7_verify().
  20. =head1 VERIFY PROCESS
  21. Normally the verify process proceeds as follows.
  22. Initially some sanity checks are performed on B<p7>. The type of B<p7> must
  23. be signedData. There must be at least one signature on the data and if
  24. the content is detached B<indata> cannot be B<NULL>.
  25. An attempt is made to locate all the signer's certificates, first looking in
  26. the B<certs> parameter (if it is not B<NULL>) and then looking in any certificates
  27. contained in the B<p7> structure itself. If any signer's certificates cannot be
  28. located the operation fails.
  29. Each signer's certificate is chain verified using the B<smimesign> purpose and
  30. the supplied trusted certificate store. Any internal certificates in the message
  31. are used as untrusted CAs. If any 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) and
  33. 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> parameter
  36. to change the default verify behaviour. Only the flag B<PKCS7_NOINTERN> is
  37. meaningful to PKCS7_get0_signers().
  38. If B<PKCS7_NOINTERN> is set the certificates in the message itself are not
  39. searched when locating the signer's certificate. This means that all the signers
  40. certificates must be in the B<certs> parameter.
  41. If the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are deleted
  42. from the content. If the content is not of type B<text/plain> then an error is
  43. returned.
  44. If B<PKCS7_NOVERIFY> is set the signer's certificates are not chain verified.
  45. If B<PKCS7_NOCHAIN> is set then the certificates contained in the message are
  46. not used as untrusted CAs. This means that the whole verify chain (apart from
  47. the signer's certificate) must be contained in the trusted store.
  48. If B<PKCS7_NOSIGS> is set then the signatures on the data are not checked.
  49. =head1 NOTES
  50. One application of B<PKCS7_NOINTERN> is to only accept messages signed by
  51. a small number of certificates. The acceptable certificates would be passed
  52. in the B<certs> parameter. In this case if the signer is not one of the
  53. certificates supplied in B<certs> then the verify will fail because the
  54. signer cannot be found.
  55. Care should be taken when modifying the default verify behaviour, for example
  56. setting B<PKCS7_NOVERIFY|PKCS7_NOSIGS> will totally disable all verification
  57. and any signed message will be considered valid. This combination is however
  58. useful if one merely wishes to write the content to B<out> and its validity
  59. is not considered important.
  60. Chain verification should arguably be performed using the signing time rather
  61. than the current time. However since the signing time is supplied by the
  62. signer it cannot be trusted without additional evidence (such as a trusted
  63. timestamp).
  64. =head1 RETURN VALUES
  65. PKCS7_verify() returns one for a successful verification and zero
  66. if an error occurs.
  67. PKCS7_get0_signers() returns all signers or B<NULL> if an error occurred.
  68. The error can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>
  69. =head1 BUGS
  70. The trusted certificate store is not searched for the signers certificate,
  71. this is primarily due to the inadequacies of the current B<X509_STORE>
  72. functionality.
  73. The lack of single pass processing and need to hold all data in memory as
  74. mentioned in PKCS7_sign() also applies to PKCS7_verify().
  75. =head1 SEE ALSO
  76. L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_sign(3)|PKCS7_sign(3)>
  77. =head1 HISTORY
  78. PKCS7_verify() was added to OpenSSL 0.9.5
  79. =cut