|  |  |  |  | 
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.