CMS_sign.pod 5.7 KB

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  1. =pod
  2. =head1 NAME
  3. CMS_sign, CMS_sign_ex - create a CMS SignedData structure
  4. =head1 SYNOPSIS
  5. #include <openssl/cms.h>
  6. CMS_ContentInfo *CMS_sign_ex(X509 *signcert, EVP_PKEY *pkey,
  7. STACK_OF(X509) *certs, BIO *data,
  8. unsigned int flags, OSSL_LIB_CTX *ctx,
  9. const char *propq);
  10. CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
  11. BIO *data, unsigned int flags);
  12. =head1 DESCRIPTION
  13. CMS_sign_ex() creates and returns a CMS SignedData structure.
  14. I<signcert> is the certificate to sign with, I<pkey> is the corresponding
  15. private key. I<certs> is an optional additional set of certificates to include
  16. in the CMS structure (for example any intermediate CAs in the chain). The
  17. library context I<libctx> and the property query I<propq> are used when
  18. retrieving algorithms from providers. Any or all of these parameters can be
  19. B<NULL>, see B<NOTES> below.
  20. The data to be signed is read from BIO B<data>.
  21. B<flags> is an optional set of flags.
  22. CMS_sign() is similar to CMS_sign_ex() but uses default values of NULL
  23. for the library context I<libctx> and the property query I<propq>.
  24. =head1 NOTES
  25. Any of the following flags (ored together) can be passed in the B<flags>
  26. parameter.
  27. Many S/MIME clients expect the signed content to include valid MIME headers. If
  28. the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are prepended
  29. to the data.
  30. If B<CMS_NOCERTS> is set the signer's certificate will not be included in the
  31. CMS_ContentInfo structure, the signer's certificate must still be supplied in
  32. the B<signcert> parameter though. This can reduce the size of the signature if
  33. the signers certificate can be obtained by other means: for example a
  34. previously signed message.
  35. The data being signed is included in the CMS_ContentInfo structure, unless
  36. B<CMS_DETACHED> is set in which case it is omitted. This is used for
  37. CMS_ContentInfo detached signatures which are used in S/MIME plaintext signed
  38. messages for example.
  39. Normally the supplied content is translated into MIME canonical format (as
  40. required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
  41. occurs. This option should be used if the supplied data is in binary format
  42. otherwise the translation will corrupt it.
  43. The SignedData structure includes several CMS signedAttributes including the
  44. signing time, the CMS content type and the supported list of ciphers in an
  45. SMIMECapabilities attribute. If B<CMS_NOATTR> is set then no signedAttributes
  46. will be used. If B<CMS_NOSMIMECAP> is set then just the SMIMECapabilities are
  47. omitted.
  48. If present the SMIMECapabilities attribute indicates support for the following
  49. algorithms in preference order: 256 bit AES, Gost R3411-94, Gost 28147-89, 192
  50. bit AES, 128 bit AES, triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2.
  51. If any of these algorithms is not available then it will not be included:
  52. for example the GOST algorithms will not be included if the GOST ENGINE is
  53. not loaded.
  54. OpenSSL will by default identify signing certificates using issuer name
  55. and serial number. If B<CMS_USE_KEYID> is set it will use the subject key
  56. identifier value instead. An error occurs if the signing certificate does not
  57. have a subject key identifier extension.
  58. If the flags B<CMS_STREAM> is set then the returned B<CMS_ContentInfo>
  59. structure is just initialized ready to perform the signing operation. The
  60. signing is however B<not> performed and the data to be signed is not read from
  61. the B<data> parameter. Signing is deferred until after the data has been
  62. written. In this way data can be signed in a single pass.
  63. If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is
  64. output to which additional signers and capabilities can be added before
  65. finalization.
  66. If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
  67. B<not> complete and outputting its contents via a function that does not
  68. properly finalize the B<CMS_ContentInfo> structure will give unpredictable
  69. results.
  70. Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
  71. PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
  72. can be performed by obtaining the streaming ASN1 B<BIO> directly using
  73. BIO_new_CMS().
  74. If a signer is specified it will use the default digest for the signing
  75. algorithm. This is B<SHA1> for both RSA and DSA keys.
  76. If B<signcert> and B<pkey> are NULL then a certificates only CMS structure is
  77. output.
  78. The function CMS_sign() is a basic CMS signing function whose output will be
  79. suitable for many purposes. For finer control of the output format the
  80. B<certs>, B<signcert> and B<pkey> parameters can all be B<NULL> and the
  81. B<CMS_PARTIAL> flag set. Then one or more signers can be added using the
  82. function CMS_sign_add1_signer(), non default digests can be used and custom
  83. attributes added. CMS_final() must then be called to finalize the
  84. structure if streaming is not enabled.
  85. =head1 BUGS
  86. Some attributes such as counter signatures are not supported.
  87. =head1 RETURN VALUES
  88. CMS_sign_ex() and CMS_sign() return either a valid CMS_ContentInfo
  89. structure or NULL if an error occurred. The error can be obtained from
  90. ERR_get_error(3).
  91. =head1 SEE ALSO
  92. L<ERR_get_error(3)>, L<CMS_verify(3)>
  93. =head1 HISTORY
  94. The B<CMS_STREAM> flag is only supported for detached data in OpenSSL 0.9.8,
  95. it is supported for embedded data in OpenSSL 1.0.0 and later.
  96. The CMS_sign_ex() method was added in OpenSSL 3.0.
  97. =head1 COPYRIGHT
  98. Copyright 2008-2020 The OpenSSL Project Authors. All Rights Reserved.
  99. Licensed under the Apache License 2.0 (the "License"). You may not use
  100. this file except in compliance with the License. You can obtain a copy
  101. in the file LICENSE in the source distribution or at
  102. L<https://www.openssl.org/source/license.html>.
  103. =cut