NAME¶
PKCS7_sign - create a PKCS#7 signedData structure
SYNOPSIS¶
#include <openssl/pkcs7.h>
PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags);
DESCRIPTION¶
PKCS7_sign() creates and returns a PKCS#7 signedData structure.
signcert is the certificate to sign with,
pkey is the
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.
flags is an optional set of flags.
NOTES¶
Any of the following flags (ored together) can be passed in the
flags
parameter.
Many S/MIME clients expect the signed content to include valid MIME headers. If
the
PKCS7_TEXT flag is set MIME headers for type
text/plain are
prepended to the data.
If
PKCS7_NOCERTS is set the signer's certificate will not be included in
the PKCS7 structure, the signer's certificate must still be supplied in the
signcert 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
PKCS7_DETACHED is set in which case it is omitted. This is used for
PKCS7 detached signatures which are used in S/MIME plaintext signed messages
for example.
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 is set
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 structure
is just initialized ready to perform the signing operation. The signing is
however
not performed and the data to be signed is not read from the
data 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 structure is
output to which additional signers and capabilities can be added before
finalization.
NOTES¶
If the flag
PKCS7_STREAM is set the returned
PKCS7 structure is
not 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(),
i2d_PKCS7_bio_stream(),
PEM_write_bio_PKCS7_stream() finalize
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,
signcert and
pkey parameters
can all be
NULL if the
PKCS7_PARTIAL flag is set. One or more
signers can be added using the function
PKCS7_sign_add_signer() .
PKCS7_final() 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 and
pkey are NULL then a certificates
only PKCS#7 structure is output.
In versions of OpenSSL before 1.0.0 the
signcert and
pkey
parameters must
NOT be NULL.
BUGS¶
Some advanced attributes such as counter signatures are not supported.
RETURN VALUES¶
PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error
occurred. The error can be obtained from
ERR_get_error(3).
SEE ALSO¶
ERR_get_error(3),
PKCS7_verify(3)
HISTORY¶
PKCS7_sign() was added to OpenSSL 0.9.5
The
PKCS7_PARTIAL flag was added in OpenSSL 1.0.0
The
PKCS7_STREAM flag was added in OpenSSL 1.0.0