PKCS7_sign (3)

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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

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

headers. If the flag is set headers for type text/plain are prepended to the data.

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 data being signed is included in the

structure, unless is set in which case it is omitted. This is used for detached signatures which are used in S/MIME plaintext signed messages for example.

Normally the supplied content is translated into

canonical format (as required by the S/MIME specifications) if 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

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.

If the flags

is set then the returned 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

flag is set a partial structure is output to which additional signers and capabilities can be added before finalization.

NOTES

If the flag is set the returned structure is not complete and outputting its contents via a function that does not properly finalize the 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

directly using BIO_new_PKCS7().

If a signer is specified it will use the default digest for the signing algorithm. This is

for both and keys.

In OpenSSL 1.0.0 the certs, signcert and pkey parameters can all be

if the 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

then a certificates only PKCS#7 structure is output.

In versions of OpenSSL before 1.0.0 the signcert and pkey parameters must

be

BUGS

Some advanced attributes such as counter signatures are not supported.

RETURN VALUES

PKCS7_sign() returns either a valid structure or 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

flag was added in OpenSSL 1.0.0

The

flag was added in OpenSSL 1.0.0