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Title "CMS_decrypt 3"
way too many mistakes in technical documents.
.nh
\fBCMS_decrypt_set1_pkey_and_peer() decrypts the CMS_ContentInfo structure cms using the private key pkey, the corresponding certificate cert, which is recommended but may be NULL, and the (optional) originator certificate peer. On success, it also records in cms the decryption key pkey, and then should be followed by \*(C`CMS_decrypt(cms, NULL, NULL, dcont, out, flags)\*(C'. This call deallocates any decryption key stored in cms.
\fBCMS_decrypt_set1_pkey() is the same as \fBCMS_decrypt_set1_pkey_and_peer() with peer being NULL.
\fBCMS_decrypt_set1_password() decrypts the CMS_ContentInfo structure cms using the secret pass of length passlen. On success, it also records in cms the decryption key used, and then should be followed by \*(C`CMS_decrypt(cms, NULL, NULL, dcont, out, flags)\*(C'. This call deallocates any decryption key stored in cms.
If cert is set to NULL all possible recipients are tried. This case however is problematic. To thwart the MMA attack (Bleichenbacher\*(Aqs attack on PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or not. If no recipient succeeds then a random symmetric key is used to decrypt the content: this will typically output garbage and may (but is not guaranteed to) ultimately return a padding error only. If CMS_decrypt() just returned an error when all recipient encrypted keys failed to decrypt an attacker could use this in a timing attack. If the special flag CMS_DEBUG_DECRYPT is set then the above behaviour is modified and an error is returned if no recipient encrypted key can be decrypted without generating a random content encryption key. Applications should use this flag with \fBextreme caution especially in automated gateways as it can leave them open to attack.
It is possible to determine the correct recipient key by other means (for example looking them up in a database) and setting them in the CMS structure in advance using the CMS utility functions such as CMS_set1_pkey(), or use CMS_decrypt_set1_password() if the recipient has a symmetric key. In these cases both cert and pkey should be set to NULL.
To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key() and CMS_RecipientInfo_decrypt() should be called before CMS_decrypt() and \fIcert and pkey set to NULL.
The following flags can be passed in the flags parameter.
If the CMS_TEXT flag is set MIME headers for type \*(C`text/plain\*(C' are deleted from the content. If the content is not of type \*(C`text/plain\*(C' then an error is returned.
The lack of single pass processing and the need to hold all data in memory as mentioned in CMS_verify() also applies to CMS_decrypt().
Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.
Indexes created Wed Apr 22 00:22:44 UTC 2026