System for generating a security document

A document identifier for a security document is generated by a computing node in a system having a unique node identifier NODE and being capable of running multiple concurrent processes, each of which have a unique process identifier APP. The node collects information for inclusion in the document, including at least a unique subject identifier SERIAL ,e.g. a serial number of a device such as a mobile telephone IMEI and concatenates this with a random value R2 e.g. generated as a decimal representation of an integer from a pseudo-random number generater. A cryptographic hash function e.g. MD5 message digest function is applied to the result and the value is then truncated e.g. using only the first eight digits. This is stored as a variable HASH. The document identifier is a concatenation of the node identifier, a first delimiter D1 e.g. -, the process identifier, the first delimiter, a first random value R1 e.g. generated as a hexadecimal representation of the current value of a microsecond timer of the node, a second delimiter D2 e.g. : and the truncated value HASH e.g. NODE, D1, APP, D1, R1, D2, HASH. This generates a secure identifier unique to the node and process being run, avoiding collision where multiple nodes or processes could generate the same document identifier.