openssl: Adjust manual pages for 1.0.1h.
[dragonfly.git] / secure / lib / libcrypto / man / CMS_decrypt.3
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124.\" ========================================================================
125.\"
126.IX Title "CMS_decrypt 3"
34240b21 127.TH CMS_decrypt 3 "2014-06-05" "1.0.1h" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
132.SH "NAME"
133.Vb 1
134\& CMS_decrypt \- decrypt content from a CMS envelopedData structure
135.Ve
136.SH "SYNOPSIS"
137.IX Header "SYNOPSIS"
138.Vb 1
139\& #include <openssl/cms.h>
140\&
141\& int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, BIO *dcont, BIO *out, unsigned int flags);
142.Ve
143.SH "DESCRIPTION"
144.IX Header "DESCRIPTION"
145\&\fICMS_decrypt()\fR extracts and decrypts the content from a \s-1CMS\s0 EnvelopedData
146structure. \fBpkey\fR is the private key of the recipient, \fBcert\fR is the
147recipient's certificate, \fBout\fR is a \s-1BIO\s0 to write the content to and
148\&\fBflags\fR is an optional set of flags.
149.PP
150The \fBdcont\fR parameter is used in the rare case where the encrypted content
151is detached. It will normally be set to \s-1NULL\s0.
152.SH "NOTES"
153.IX Header "NOTES"
154\&\fIOpenSSL_add_all_algorithms()\fR (or equivalent) should be called before using this
155function or errors about unknown algorithms will occur.
156.PP
157Although the recipients certificate is not needed to decrypt the data it is
158needed to locate the appropriate (of possible several) recipients in the \s-1CMS\s0
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159structure.
160.PP
161If \fBcert\fR is set to \s-1NULL\s0 all possible recipients are tried. This case however
162is problematic. To thwart the \s-1MMA\s0 attack (Bleichenbacher's attack on
163\&\s-1PKCS\s0 #1 v1.5 \s-1RSA\s0 padding) all recipients are tried whether they succeed or
164not. If no recipient succeeds then a random symmetric key is used to decrypt
165the content: this will typically output garbage and may (but is not guaranteed
166to) ultimately return a padding error only. If \fICMS_decrypt()\fR just returned an
167error when all recipient encrypted keys failed to decrypt an attacker could
168use this in a timing attack. If the special flag \fB\s-1CMS_DEBUG_DECRYPT\s0\fR is set
169then the above behaviour is modified and an error \fBis\fR returned if no
170recipient encrypted key can be decrypted \fBwithout\fR generating a random
171content encryption key. Applications should use this flag with
172\&\fBextreme caution\fR especially in automated gateways as it can leave them
173open to attack.
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174.PP
175It is possible to determine the correct recipient key by other means (for
176example looking them up in a database) and setting them in the \s-1CMS\s0 structure
177in advance using the \s-1CMS\s0 utility functions such as \fICMS_set1_pkey()\fR. In this
178case both \fBcert\fR and \fBpkey\fR should be set to \s-1NULL\s0.
179.PP
180To process KEKRecipientInfo types \fICMS_set1_key()\fR or \fICMS_RecipientInfo_set0_key()\fR
181and \fICMS_ReceipientInfo_decrypt()\fR should be called before \fICMS_decrypt()\fR and
182\&\fBcert\fR and \fBpkey\fR set to \s-1NULL\s0.
183.PP
184The following flags can be passed in the \fBflags\fR parameter.
185.PP
186If the \fB\s-1CMS_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are deleted
187from the content. If the content is not of type \fBtext/plain\fR then an error is
188returned.
189.SH "RETURN VALUES"
190.IX Header "RETURN VALUES"
191\&\fICMS_decrypt()\fR returns either 1 for success or 0 for failure.
192The error can be obtained from \fIERR_get_error\fR\|(3)
193.SH "BUGS"
194.IX Header "BUGS"
195The lack of single pass processing and the need to hold all data in memory as
196mentioned in \fICMS_verify()\fR also applies to \fICMS_decrypt()\fR.
197.SH "SEE ALSO"
198.IX Header "SEE ALSO"
199\&\fIERR_get_error\fR\|(3), \fICMS_encrypt\fR\|(3)
200.SH "HISTORY"
201.IX Header "HISTORY"
202\&\fICMS_decrypt()\fR was added to OpenSSL 0.9.8