add a signer to a SignedData
X509 *signcert, EVP_PKEY *pkey,
const EVP_MD *md, int
adds a signer with certificate signcert and private
key pkey using message digest md
to a PKCS7 signed data structure
The PKCS7 structure should be obtained from
an initial call to
PKCS7_sign(3) with the flag
or, in the case or re-signing, a valid PKCS7 signed
If the md parameter is
NULL, then the default digest for the public key
algorithm will be used.
PKCS7_REUSE_DIGEST flag is set,
PKCS7 structure is not complete and
must be finalized either by streaming (if applicable) or by a call to
The main purpose of this function is to provide finer control over a PKCS#7 signed data structure where the simpler PKCS7_sign(3) function defaults are not appropriate, for example if multiple signers or non default digest algorithms are needed.
Any of the following flags (OR'ed together) can be passed in the flags parameter.
PKCS7_REUSE_DIGEST is set, then an
attempt is made to copy the content digest value from the
PKCS7 structure: to add a signer to an existing
structure. An error occurs if a matching digest value cannot be found to
copy. The returned PKCS7 structure will be valid and
finalized when this flag is set.
PKCS7_PARTIAL is set in addition to
PKCS7_REUSE_DIGEST, then the
PKCS7_SIGNER_INO structure will not be finalized, so
additional attributes can be added. In this case an explicit call to
is needed to finalize it.
PKCS7_NOCERTS is set, the signer's
certificate will not be included in the PKCS7
structure, though the signer's certificate must still be supplied in the
signcert parameter. 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 signedData structure includes several PKCS#7
authenticatedAttributes 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.
returns an internal pointer to the PKCS7_SIGNER_INFO
structure just added, which can be used to set additional attributes with
the functions described in
PKCS7_add_attribute(3) before it is finalized.
PKCS7_sign_add_signer() returns an
internal pointer to the PKCS7_SIGNER_INFO structure
just added or
NULL if an error occurs. In some cases
of failure, the reason can be determined with
EVP_DigestInit(3), PKCS7_add_attribute(3), PKCS7_final(3), PKCS7_get_signer_info(3), PKCS7_new(3), PKCS7_sign(3)
PKCS7_sign_add_signer() first appeared in
OpenSSL 1.0.0 and has been available since OpenBSD