This part of ISO/IEC 9796 specifies three digital signature schemes giving message recovery, two of which are deterministic (non-randomized) and one of which is randomized. The security of all three schemes is based on the difficulty of factorizing large numbers. All three schemes can provide either total or partial message recovery. The method for key production for the three signature schemes is specified in this part of ISO/IEC 9796. However, techniques for key management and for random number generation (as required for the randomized signature scheme), are outside the scope of this part of ISO/IEC 9796. Users of this standard are, wherever possible, recommended to adopt the second mechanism (Digital signature scheme 2). However, in environments where generation of random variables by the signer is deemed infeasible, then Digital signature scheme 3 is recommended. Digital signature scheme 1 shall only be used in environments where compatibility is required with systems implementing the first edition of this standard. However, Digital signature scheme 1 is only compatible with systems implementing the first edition of this standard that use hashcodes of at least 160 bits.