PKCS7_sign - create a PKCS#7 signedData structure
PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags);
creates and returns a PKCS#7 signedData structure.
is the certificate to sign with, pkey
corresponsding private key. certs
is an optional additional set of
certificates to include in the PKCS#7 structure (for example any intermediate
CAs in the chain).
The data to be signed is read from BIO data
is an optional set of flags.
Any of the following flags (ored together) can be passed in the flags
Many S/MIME clients expect the signed content to include valid MIME headers. If
flag is set MIME headers for type text/plain
prepended to the data.
is set the signer's certificate will not be included in
the PKCS7 structure, the signer's certificate must still be supplied in the
parameter though. This can reduce the size of the signature if
the signers certificate can be obtained by other means: for example a
previously signed message.
The data being signed is included in the PKCS7 structure, unless
is set in which case it is omitted. This is used for
PKCS7 detached signatures which are used in S/MIME plaintext signed messages
Normally the supplied content is translated into MIME canonical format (as
required by the S/MIME specifications) if PKCS7_BINARY
is set no
translation occurs. This option should be used if the supplied data is in
binary format otherwise the translation will corrupt it.
The signedData structure includes several PKCS#7 autenticatedAttributes
including the signing time, the PKCS#7 content type and the supported list of
ciphers in an SMIMECapabilities attribute. If PKCS7_NOATTR
is set then
no authenticatedAttributes will be used. If PKCS7_NOSMIMECAP
then just the SMIMECapabilities are omitted.
If present the SMIMECapabilities attribute indicates support for the following
algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any of
these algorithms is disabled then it will not be included.
If the flags PKCS7_STREAM
is set then the returned PKCS7
is just initialized ready to perform the signing operation. The signing is
performed and the data to be signed is not read from the
parameter. Signing is deferred until after the data has been
written. In this way data can be signed in a single pass.
If the PKCS7_PARTIAL
flag is set a partial PKCS7
output to which additional signers and capabilities can be added before
If the flag PKCS7_STREAM
is set the returned PKCS7
complete and outputting its contents via a function that does not
properly finalize the PKCS7
structure will give unpredictable results.
Several functions including SMIME_write_PKCS7()
the structure. Alternatively finalization can be performed by obtaining the
streaming ASN1 BIO
directly using BIO_new_PKCS7()
If a signer is specified it will use the default digest for the signing
algorithm. This is SHA1
for both RSA and DSA keys.
In OpenSSL 1.0.0 the certs
can all be NULL
if the PKCS7_PARTIAL
flag is set. One or more
signers can be added using the function
must also be called to finalize the
structure if streaming is not enabled. Alternative signing digests can also be
specified using this method.
In OpenSSL 1.0.0 if signcert
are NULL then a certificates
only PKCS#7 structure is output.
In versions of OpenSSL before 1.0.0 the signcert
parameters must NOT
Some advanced attributes such as counter signatures are not supported.
returns either a valid PKCS7 structure or NULL if an error
occurred. The error can be obtained from ERR_get_error(3)
was added to OpenSSL 0.9.5
flag was added in OpenSSL 1.0.0
flag was added in OpenSSL 1.0.0