[AKL83] is the classic paper on digital signatures and is still highly relevant. A more recent, and excellent, survey is [MITC92].
AKL83 Akl, S. "Digital Signatures: A Tutorial Survey." Computer, February 1983.MITC92 Mitchell, C.; Piper, F. ; and Wild, P. "Digital Signatures." In [SIMM92a].
AKL83 Akl, S. "Digital Signatures: A Tutorial Survey." Computer, February 1983.
MITC92 Mitchell, C.; Piper, F. ; and Wild, P. "Digital Signatures." In [SIMM92a].
Digital Signatures: NIST page with information on NIST-approved digital signature options