5 PKCS7_sign - create a PKCS#7 signedData structure
9 PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags);
13 PKCS7_sign() creates and returns a PKCS#7 signedData structure. B<signcert>
14 is the certificate to sign with, B<pkey> is the corresponsding private key.
15 B<certs> is an optional additional set of certificates to include in the
16 PKCS#7 structure (for example any intermediate CAs in the chain).
18 The data to be signed is read from BIO B<data>.
20 B<flags> is an optional set of flags.
24 Any of the following flags (ored together) can be passed in the B<flags> parameter.
26 Many S/MIME clients expect the signed content to include valid MIME headers. If
27 the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are prepended
30 If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
31 PKCS7 structure, the signer's certificate must still be supplied in the B<signcert>
32 parameter though. This can reduce the size of the signature if the signers certificate
33 can be obtained by other means: for example a previously signed message.
35 The data being signed is included in the PKCS7 structure, unless B<PKCS7_DETACHED>
36 is set in which case it is omitted. This is used for PKCS7 detached signatures
37 which are used in S/MIME plaintext signed messages for example.
39 Normally the supplied content is translated into MIME canonical format (as required
40 by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation occurs. This
41 option should be used if the supplied data is in binary format otherwise the translation
44 The signedData structure includes several PKCS#7 autenticatedAttributes including
45 the signing time, the PKCS#7 content type and the supported list of ciphers in
46 an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no authenticatedAttributes
47 will be used. If B<PKCS7_NOSMIMECAP> is set then just the SMIMECapabilities are
50 If present the SMIMECapabilities attribute indicates support for the following
51 algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any
52 of these algorithms is disabled then it will not be included.
54 If the flags B<PKCS7_PARTSIGN> is set then the returned B<PKCS7> structure
55 is just initialized ready to perform the signing operation. The signing
56 is however B<not> performed and the data to be signed is not read from
57 the B<data> parameter. Signing is deferred until after the data has been
58 written. In this way data can be signed in a single pass. Currently the
59 flag B<PKCS7_DETACHED> B<must> also be set.
63 Currently the flag B<PKCS7_PARTSIGN> is only supported for detached
64 data. If this flag is set the returned B<PKCS7> structure is B<not>
65 complete and outputting its contents via a function that does not
66 properly finalize the B<PKCS7> structure will give unpredictable
69 At present only the SMIME_write_PKCS7() function properly finalizes the
74 PKCS7_sign() is somewhat limited. It does not support multiple signers, some
75 advanced attributes such as counter signatures are not supported.
77 The SHA1 digest algorithm is currently always used.
79 When the signed data is not detached it will be stored in memory within the
80 B<PKCS7> structure. This effectively limits the size of messages which can be
81 signed due to memory restraints. There should be a way to sign data without
82 having to hold it all in memory, this would however require fairly major
83 revisions of the OpenSSL ASN1 code.
88 PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error occurred.
89 The error can be obtained from ERR_get_error(3).
93 L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_verify(3)|PKCS7_verify(3)>
97 PKCS7_sign() was added to OpenSSL 0.9.5
99 The B<PKCS7_PARTSIGN> flag was added in OpenSSL 0.9.8