|  |  |  |  | 
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 statusvariable 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 statusvariable 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.