Edit File: CMS_decrypt.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" .Vb 1 \& CMS_decrypt \- decrypt content from a CMS envelopedData structure .Ve .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/cms.h> \& \& int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, BIO *dcont, BIO *out, unsigned int flags); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBCMS_decrypt()\fR extracts and decrypts the content from a \s-1CMS\s0 EnvelopedData structure. \fBpkey\fR is the private key of the recipient, \fBcert\fR is the recipient's certificate, \fBout\fR is a \s-1BIO\s0 to write the content to and \&\fBflags\fR is an optional set of flags. .PP The \fBdcont\fR parameter is used in the rare case where the encrypted content is detached. It will normally be set to \s-1NULL.\s0 .SH "NOTES" .IX Header "NOTES" \&\fBOpenSSL_add_all_algorithms()\fR (or equivalent) should be called before using this function or errors about unknown algorithms will occur. .PP Although the recipients certificate is not needed to decrypt the data it is needed to locate the appropriate (of possible several) recipients in the \s-1CMS\s0 structure. .PP If \fBcert\fR is set to \s-1NULL\s0 all possible recipients are tried. This case however is problematic. To thwart the \s-1MMA\s0 attack (Bleichenbacher's attack on \&\s-1PKCS\s0 #1 v1.5 \s-1RSA\s0 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 \fBCMS_decrypt()\fR 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 \fB\s-1CMS_DEBUG_DECRYPT\s0\fR is set then the above behaviour is modified and an error \fBis\fR returned if no recipient encrypted key can be decrypted \fBwithout\fR generating a random content encryption key. Applications should use this flag with \&\fBextreme caution\fR especially in automated gateways as it can leave them open to attack. .PP 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 \s-1CMS\s0 structure in advance using the \s-1CMS\s0 utility functions such as \fBCMS_set1_pkey()\fR. In this case both \fBcert\fR and \fBpkey\fR should be set to \s-1NULL.\s0 .PP To process KEKRecipientInfo types \fBCMS_set1_key()\fR or \fBCMS_RecipientInfo_set0_key()\fR and \fBCMS_ReceipientInfo_decrypt()\fR should be called before \fBCMS_decrypt()\fR and \&\fBcert\fR and \fBpkey\fR set to \s-1NULL.\s0 .PP The following flags can be passed in the \fBflags\fR parameter. .PP If the \fB\s-1CMS_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are deleted from the content. If the content is not of type \fBtext/plain\fR then an error is returned. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBCMS_decrypt()\fR returns either 1 for success or 0 for failure. The error can be obtained from \fBERR_get_error\fR\|(3) .SH "BUGS" .IX Header "BUGS" The lack of single pass processing and the need to hold all data in memory as mentioned in \fBCMS_verify()\fR also applies to \fBCMS_decrypt()\fR. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBERR_get_error\fR\|(3), \fBCMS_encrypt\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" \&\fBCMS_decrypt()\fR was added to OpenSSL 0.9.8