This part of ISO/IEC 9796 specifies six digital signature schemes giving message recovery. The security of these schemes is based on the difficulty of the discrete logarithm problem, which is defined on a finite field or an elliptic curve over a finite field. This part of ISO/IEC 9796 also defines an optional control field in the hash-token, which can provide added security to the signature. This part of ISO/IEC 9796 specifies randomized mechanisms. The mechanisms specified in this part of ISO/IEC 9796 give either total or partial message recovery. NOTE For discrete logarithm based digital signature schemes with appendix, see ISO/IEC 14888-3.