1. A method of generating a cryptographic validation value for use in authenticating data, the method performed by a computer system comprising a processor and a memory encoded with program instructions that, when executed by the processor, cause the system to perform the method, the method including: receiving a piece of encrypted data; obtaining an input validation value from the encrypted data; dividing, by the processor, the input validation value into a first segment and a second segment; using at least a first function to combine the first segment with a first input from a cryptographic cipher function, whereby the first function produces a first result; using at least a second function to combine the second segment with a second input from the cryptographic cipher function, whereby the second function produces a second result; generating, by the processor, a first transformed result by performing at least a first transformation on a first value, the first value being derived, at least in part, from the first result; generating, by the processor, a second transformed result by performing at least a second transformation on a second value, the second value being derived, at least in part, from the second result; forming, by a processor, an output validation value by combining a third segment and a fourth segment, the third segment being derived, at least in part, from the first transformed result, and the fourth segment being derived, at least in part, from the second transformed result; and using the output validation value to authenticate the piece of encrypted data.