5 PKCS7_sign - create a PKCS#7 signedData structure
9 #include <openssl/pkcs7.h>
11 PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags);
15 PKCS7_sign() creates and returns a PKCS#7 signedData structure. B<signcert>
16 is the certificate to sign with, B<pkey> is the corresponsding private key.
17 B<certs> is an optional additional set of certificates to include in the
18 PKCS#7 structure (for example any intermediate CAs in the chain).
20 The data to be signed is read from BIO B<data>.
22 B<flags> is an optional set of flags.
26 Any of the following flags (ored together) can be passed in the B<flags> parameter.
28 Many S/MIME clients expect the signed content to include valid MIME headers. If
29 the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are prepended
32 If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
33 PKCS7 structure, the signer's certificate must still be supplied in the B<signcert>
34 parameter though. This can reduce the size of the signature if the signers certificate
35 can be obtained by other means: for example a previously signed message.
37 The data being signed is included in the PKCS7 structure, unless B<PKCS7_DETACHED>
38 is set in which case it is omitted. This is used for PKCS7 detached signatures
39 which are used in S/MIME plaintext signed messages for example.
41 Normally the supplied content is translated into MIME canonical format (as required
42 by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation occurs. This
43 option should be used if the supplied data is in binary format otherwise the translation
46 The signedData structure includes several PKCS#7 autenticatedAttributes including
47 the signing time, the PKCS#7 content type and the supported list of ciphers in
48 an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no authenticatedAttributes
49 will be used. If B<PKCS7_NOSMIMECAP> is set then just the SMIMECapabilities are
52 If present the SMIMECapabilities attribute indicates support for the following
53 algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any
54 of these algorithms is disabled then it will not be included.
56 If the flags B<PKCS7_PARTSIGN> is set then the returned B<PKCS7> structure
57 is just initialized ready to perform the signing operation. The signing
58 is however B<not> performed and the data to be signed is not read from
59 the B<data> parameter. Signing is deferred until after the data has been
60 written. In this way data can be signed in a single pass. Currently the
61 flag B<PKCS7_DETACHED> B<must> also be set.
65 Currently the flag B<PKCS7_PARTSIGN> is only supported for detached
66 data. If this flag is set the returned B<PKCS7> structure is B<not>
67 complete and outputting its contents via a function that does not
68 properly finalize the B<PKCS7> structure will give unpredictable
71 At present only the SMIME_write_PKCS7() function properly finalizes the
76 PKCS7_sign() is somewhat limited. It does not support multiple signers, some
77 advanced attributes such as counter signatures are not supported.
79 The SHA1 digest algorithm is currently always used.
81 When the signed data is not detached it will be stored in memory within the
82 B<PKCS7> structure. This effectively limits the size of messages which can be
83 signed due to memory restraints. There should be a way to sign data without
84 having to hold it all in memory, this would however require fairly major
85 revisions of the OpenSSL ASN1 code.
90 PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error occurred.
91 The error can be obtained from ERR_get_error(3).
95 L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_verify(3)|PKCS7_verify(3)>
99 PKCS7_sign() was added to OpenSSL 0.9.5
101 The B<PKCS7_PARTSIGN> flag was added in OpenSSL 0.9.8