An apparatus, configured to perform a hash operation, the apparatus comprising: a microprocessor, configured to execute an application program that is fetched from a memory, and configured to execute an instruction within said application program that directs said microprocessor to perform the hash operation, wherein said microprocessor comprises: a hash unit (316,617), configured to execute a plurality of hash computations on each of said one or more message blocks to generate a corresponding intermediate hash value, wherein a last intermediate hash value that is computed for a last message block after processing all previous message blocks comprises a message digest corresponding to said one or more message blocks. characterised in that said instruction comprises: an opcode field, configured to prescribe that the microprocessor accomplish the hash operation; a hash mode field that specifies a prescribed hash mode to be employed by the hash unit in accomplishing the hash operation; and a repeat prefix field, coupled to said opcode field, configured to indicate that the hash operation prescribed by said instruction is to be accomplished on one or more message blocks. a microprocessor, configured to execute an application program that is fetched from a memory, and configured to execute an instruction within said application program that directs said microprocessor to perform the hash operation, wherein said microprocessor comprises: a hash unit (316,617), configured to execute a plurality of hash computations on each of said one or more message blocks to generate a corresponding intermediate hash value, wherein a last intermediate hash value that is computed for a last message block after processing all previous message blocks comprises a message digest corresponding to said one or more message blocks. characterised in that said instruction comprises: an opcode field, configured to prescribe that the microprocessor accomplish the hash operation; a hash mode field that specifies a prescribed hash mode to be employed by the hash unit in accomplishing the hash operation; and a repeat prefix field, coupled to said opcode field, configured to indicate that the hash operation prescribed by said instruction is to be accomplished on one or more message blocks. a hash unit (316,617), configured to execute a plurality of hash computations on each of said one or more message blocks to generate a corresponding intermediate hash value, wherein a last intermediate hash value that is computed for a last message block after processing all previous message blocks comprises a message digest corresponding to said one or more message blocks. characterised in that said instruction comprises: an opcode field, configured to prescribe that the microprocessor accomplish the hash operation; a hash mode field that specifies a prescribed hash mode to be employed by the hash unit in accomplishing the hash operation; and a repeat prefix field, coupled to said opcode field, configured to indicate that the hash operation prescribed by said instruction is to be accomplished on one or more message blocks. an opcode field, configured to prescribe that the microprocessor accomplish the hash operation; a hash mode field that specifies a prescribed hash mode to be employed by the hash unit in accomplishing the hash operation; and a repeat prefix field, coupled to said opcode field, configured to indicate that the hash operation prescribed by said instruction is to be accomplished on one or more message blocks.