A computer-implemented method of facilitating processing in a computing environment , the computer-implemented method comprising: obtaining , by at least one processor, an instruction to be executed, the instruction comprising a Compute Last Message Digest SHA Keccak instruction used to process one or more last blocks of a message to produce a message digest to be used in authentication of the message; and, executing the instruction; the method being characterized by the executing including: distinguishing between two conditions at a beginning of execution of the instruction to ensure a padding operation for the message is performed once, the two conditions including the instruction has already performed padding for the message and is continuing with extendable-output function, XOF, generation following a previous partial completion, and a null operand message is specified but padding has not yet been performed for the message, the distinguishing comprising checking a padding state control of the instruction to determine whether padding has been performed for the message, the padding state control being an input bit to the instruction; performing a first action based on the checking indicating that padding has been performed for the message and that the input bit is set to one value; and, performing a second action, different from the first action, based on the checking indicating that padding has not been performed for the message and that the input bit is set to another value; wherein the executing further comprises determining , based on the padding state control indicating padding has been performed and based on the instruction beginning execution, whether a length of the message is nonzero, and indicating an exception based on the determining indicating the length is nonzero, the padding state control indicating padding has been performed, and the instruction beginning execution. distinguishing between two conditions at a beginning of execution of the instruction to ensure a padding operation for the message is performed once, the two conditions including the instruction has already performed padding for the message and is continuing with extendable-output function, XOF, generation following a previous partial completion, and a null operand message is specified but padding has not yet been performed for the message, the distinguishing comprising checking a padding state control of the instruction to determine whether padding has been performed for the message, the padding state control being an input bit to the instruction; performing a first action based on the checking indicating that padding has been performed for the message and that the input bit is set to one value; and, performing a second action, different from the first action, based on the checking indicating that padding has not been performed for the message and that the input bit is set to another value; wherein the executing further comprises determining , based on the padding state control indicating padding has been performed and based on the instruction beginning execution, whether a length of the message is nonzero, and indicating an exception based on the determining indicating the length is nonzero, the padding state control indicating padding has been performed, and the instruction beginning execution. <EOS>