CMS_encrypt.pod 3.5 KB

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  1. =pod
  2. =head1 NAME
  3. CMS_encrypt - create a CMS envelopedData structure
  4. =head1 SYNOPSIS
  5. #include <openssl/cms.h>
  6. CMS_ContentInfo *CMS_encrypt(STACK_OF(X509) *certs, BIO *in, const EVP_CIPHER *cipher, unsigned int flags);
  7. =head1 DESCRIPTION
  8. CMS_encrypt() creates and returns a CMS EnvelopedData structure. B<certs>
  9. is a list of recipient certificates. B<in> is the content to be encrypted.
  10. B<cipher> is the symmetric cipher to use. B<flags> is an optional set of flags.
  11. =head1 NOTES
  12. Only certificates carrying RSA keys are supported so the recipient certificates
  13. supplied to this function must all contain RSA public keys, though they do not
  14. have to be signed using the RSA algorithm.
  15. EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use
  16. because most clients will support it.
  17. The algorithm passed in the B<cipher> parameter must support ASN1 encoding of
  18. its parameters.
  19. Many browsers implement a "sign and encrypt" option which is simply an S/MIME
  20. envelopedData containing an S/MIME signed message. This can be readily produced
  21. by storing the S/MIME signed message in a memory BIO and passing it to
  22. CMS_encrypt().
  23. The following flags can be passed in the B<flags> parameter.
  24. If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are
  25. prepended to the data.
  26. Normally the supplied content is translated into MIME canonical format (as
  27. required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
  28. occurs. This option should be used if the supplied data is in binary format
  29. otherwise the translation will corrupt it. If B<CMS_BINARY> is set then
  30. B<CMS_TEXT> is ignored.
  31. OpenSSL will by default identify recipient certificates using issuer name
  32. and serial number. If B<CMS_USE_KEYID> is set it will use the subject key
  33. identifier value instead. An error occurs if all recipient certificates do not
  34. have a subject key identifier extension.
  35. If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is
  36. returned suitable for streaming I/O: no data is read from the BIO B<in>.
  37. If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is
  38. returned to which additional recipients and attributes can be added before
  39. finalization.
  40. The data being encrypted is included in the CMS_ContentInfo structure, unless
  41. B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in
  42. practice and is not supported by SMIME_write_CMS().
  43. =head1 NOTES
  44. If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
  45. B<not> complete and outputting its contents via a function that does not
  46. properly finalize the B<CMS_ContentInfo> structure will give unpredictable
  47. results.
  48. Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
  49. PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
  50. can be performed by obtaining the streaming ASN1 B<BIO> directly using
  51. BIO_new_CMS().
  52. The recipients specified in B<certs> use a CMS KeyTransRecipientInfo info
  53. structure. KEKRecipientInfo is also supported using the flag B<CMS_PARTIAL>
  54. and CMS_add0_recipient_key().
  55. The parameter B<certs> may be NULL if B<CMS_PARTIAL> is set and recipients
  56. added later using CMS_add1_recipient_cert() or CMS_add0_recipient_key().
  57. =head1 RETURN VALUES
  58. CMS_encrypt() returns either a CMS_ContentInfo structure or NULL if an error
  59. occurred. The error can be obtained from ERR_get_error(3).
  60. =head1 SEE ALSO
  61. L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_decrypt(3)|CMS_decrypt(3)>
  62. =head1 HISTORY
  63. CMS_decrypt() was added to OpenSSL 0.9.8
  64. The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0.
  65. =cut