Factors that resist pohlig &: The attack of Herman algorithm. M should generally use the hash value of information (such as SHA algorithm). The security of ElGamal mainly depends on P and G, and if it is not properly selected, the signature will be easily forged. It is necessary to ensure that G is irreducible as a big prime factor of p- 1. D. Bleichenbache's "Generating Gamal Signature Without Knowing the Key" mentioned some attack methods and countermeasures. One of the shortcomings of ElGamal is that the ciphertext has multiplied.

The DSA (digital signature algorithm) algorithm of American DSS (digital signature standard) is realized by ElGamal algorithm.

Change.