PKCS7_sign_add_signer (3)

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NAME

PKCS7_sign_add_signer - add a signer PKCS7 signed data structure.

SYNOPSIS

 #include <openssl/pkcs7.h>

 PKCS7_SIGNER_INFO *PKCS7_sign_add_signer(PKCS7 *p7, X509 *signcert, EVP_PKEY *pkey, const EVP_MD *md, int flags);

DESCRIPTION

PKCS7_sign_add_signer() adds a signer with certificate signcert and private key pkey using message digest md to a signed data structure p7.

The

structure should be obtained from an initial call to PKCS7_sign() with the flag set or in the case or re-signing a valid signed data structure.

If the md parameter is

then the default digest for the public key algorithm will be used.

Unless the

flag is set the returned structure is not complete and must be finalized either by streaming (if applicable) or a call to PKCS7_final().

NOTES

The main purpose of this function is to provide finer control over a PKCS#7 signed data structure where the simpler PKCS7_sign() function defaults are not appropriate. For example if multiple signers or non default digest algorithms are needed.

Any of the following flags (ored together) can be passed in the flags parameter.

If

is set then an attempt is made to copy the content digest value from the struture: to add a signer to an existing structure. An error occurs if a matching digest value cannot be found to copy. The returned structure will be valid and finalized when this flag is set.

If

is set in addition to then the structure will not be finalized so additional attributes can be added. In this case an explicit call to PKCS7_SIGNER_INFO_sign() is needed to finalize it.

If

is set the signer's certificate will not be included in the 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 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

is set then no authenticatedAttributes will be used. If is set then just the SMIMECapabilities are omitted.

If present the SMIMECapabilities attribute indicates support for the following algorithms: triple

bit bit and 40 bit If any of these algorithms is disabled then it will not be included.

PKCS7_sign_add_signers() returns an internal pointer to the

structure just added, this can be used to set additional attributes before it is finalized.

RETURN VALUES

PKCS7_sign_add_signers() returns an internal pointer to the structure just added or if an error occurs.

SEE ALSO

ERR_get_error(3), PKCS7_sign(3), PKCS7_final(3),

HISTORY

PPKCS7_sign_add_signer() was added to OpenSSL 1.0.0