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The cryptographic transforms (digests, signatures and encryption)
implementation is the main goal of "xmlsec-<crypto>" library.
Most of the cryptographic transforms
use default pushBin and popBin
methods and provide custom execute method.
The binary transform execute method
processes data from the input buffer
inBuf and pushes results to
outBuf. The transform should try to
consume and remove data from inBuf buffer
as soon as the data became available. However, it might happen
that current data size in the input buffer is not enough (for example,
RSA-PKCS1 algorithm requires that all the data are available in
one buffer). In this case, transform might keep the data in the
input buffer till the next call to
execute
method. The "last" parameter of the
execute
indicates that transform MUST process all the data in the input buffer
and return as much as possible in the output buffer. The
execute method
might be called multiple times with non-zero "last" parameter until
the transforms returns nothing
in the output buffer. In addition, the transform implementation is
responsible for managing the transform status
variable.
Table 2. Typical transform status managing.
| xmlSecTransformStatusNone | Transform initializes itself (for example, cipher transform
generates or reads IV) and sets status
variable to xmlSecTransformStatusWorking. |
| xmlSecTransformStatusWorking | Transform process the next (if "last" parameter is zero) or
last block of data (if "last" parameter is non-zero).
When transform returns all the data, it sets the
status variable to
xmlSecTransformStatusFinished. |
| xmlSecTransformStatusFinished | Transform returns no data to indicate that it finished processing. |
In adition to execute methods, signature, hmac or digest transforms MUST implement verify method. The verify method is called after transform execution is finished. The verify method implementation must set the "status" member to xmlSecTransformStatusOk if signature, hmac or digest is successfully verified or to xmlSecTransformStatusFail otherwise.
The transforms that require a key (signature or encryption transforms, for example) MUST imlpement setKeyReq (prepares the key requirements for key search) and setKey (sets the key in the transform) methods.