NAME
PKCS7_dataInit
—
construct a BIO chain for adding or
retrieving content
SYNOPSIS
#include
<openssl/pkcs7.h>
BIO *
PKCS7_dataInit
(PKCS7 *p7,
BIO *indata);
DESCRIPTION
PKCS7_dataInit
()
constructs a BIO chain in preparation for putting data into or retrieving
data out of p7. Depending on the
contentType of p7, the created
chain starts with:
- for SignedData:
- one or more BIO_f_md(3) message digest filters
- for EnvelopedData:
- one BIO_f_cipher(3) encryption filter
- for SignedAndEnvelopedData:
- one or more BIO_f_md(3) message digest filters followed by one BIO_f_cipher(3) encryption filter
- for DigestedData:
- one BIO_f_md(3) message digest filter
- for arbitrary data:
- no filter BIO
One additional BIO is appended to the end of the chain, depending on the first condition that holds in the following list:
- indata
- if the indata argument is not
NULL
. This only makes sense while verifying a detached signature, in which case indata is expected to supply the content associated with the detached signature. - BIO_s_null(3)
- if the contentType of p7 is SignedData and it is configured to contain a detached signature. This only makes sense while creating the detached signature.
- BIO_new_mem_buf(3)
- when reading from a SignedData or
DigestedData object.
PKCS7_dataInit
() attaches the end of the chain to the nested content of p7. - BIO_s_mem(3)
- otherwise. This is the most common case while writing data to p7. PKCS7_dataFinal(3) can later be used to transfer the data from the memory BIO into p7.
Adding content
Before calling PKCS7_dataInit
() in order
to add content,
PKCS7_new(3),
PKCS7_set_type(3), and
PKCS7_content_new(3) are typically required to create
p7, to choose its desired type, and to allocate the
nested ContentInfo structure. Alternatively, for
SignedData,
PKCS7_sign(3) can be used with the
PKCS7_PARTIAL
or
PKCS7_STREAM
flags or for
EnvelopedData,
PKCS7_encrypt(3) with the
PKCS7_STREAM
flag.
After calling
PKCS7_dataInit
(),
the desired data can be written into the returned BIO,
BIO_flush(3) can be called on it,
PKCS7_dataFinal(3) can be used to transfer the processed data
from the returned memory BIO to the p7 structure, and
the chain can finally be destroyed with
BIO_free_all(3).
While
PKCS7_dataInit
()
does support the EnvelopedData and
SignedAndEnvelopedData types, using it for these types
is awkward and error prone except when using
PKCS7_encrypt(3) for the setup because
PKCS7_content_new(3) does not support these two types. So in
addition to creating p7 itself and setting its type,
the nested ContentInfo structure also needs to be
constructed with
PKCS7_new(3) and
PKCS7_set_type(3) and manually inserted into the correct
field of the respective sub-structure of p7.
Retrieving content
PKCS7_dataInit
() can also be called on a
fully populated object of type SignedData or
DigestedData. After that,
BIO_read(3) can be used to retrieve data from it. In this use case,
do not call
PKCS7_dataFinal(3); simply proceed directly to
BIO_free_all(3) after reading the data.
RETURN VALUES
PKCS7_dataInit
() returns a BIO chain on
success or NULL
on failure. It fails if
p7 is NULL
, if the
content field of p7 is empty, if
the contentType of p7 is
unsupported, if a cipher is required but none is configured, or if any
required operation fails, for example due to lack of memory or for various
other reasons.
SEE ALSO
BIO_new(3), BIO_read(3), PKCS7_content_new(3), PKCS7_dataFinal(3), PKCS7_encrypt(3), PKCS7_final(3), PKCS7_new(3), PKCS7_set_type(3), PKCS7_sign(3)
HISTORY
PKCS7_dataInit
() first appeared in SSLeay
0.8.1 and has been available since OpenBSD 2.4.
CAVEATS
This function does not support EncryptedData.
BUGS
If p7 is a fully populated structure
containing EnvelopedData,
SignedAndEnvelopedData, or arbitrary data,
PKCS7_dataInit
() returns a BIO chain that ultimately
reads from an empty memory BIO, so reading from it will instantly return an
end-of-file indication rather than reading the actual data contained in
p7.