Just to make sure about ElGamal Digital Signature, lecture 2 ,, slide 74 , M is the Digest value or the message itself?

if it is the digest , then do we have the free choice to choose between MD5 or SHA , or A symmetric-key block cipher?

so ElGamal  does not use any Hash Algorithm like MD or SHA ? .as we heard in slide 58 , we have two different approaches for compression function :

, "form scratch" ( like MD or SHA)    or]

"A symmetric-key block cipher serves as a compression function" ,

but Elgamal is a asymmetric key crypto system , not a symmetric one . I am still confused about it.