question: public HMACT64 ( byte [ ] key ) { super ( "HMACT64" ) ; int length = Math . min ( key . length , BLOCK_LENGTH ) ; for ( int i = 0 ; i < length ; i ++ ) { ipad [ i ] = ( byte ) ( key [ i ] ^ IPAD ) ; opad [ i ] = ( byte ) ( key [ i ] ^ OPAD ) ; } for ( int i = length ; i < BLOCK_LENGTH ; i ++ ) { ipad [ i ] = IPAD ; opad [ i ] = OPAD ; } try { md5 = MessageDigest . getInstance ( "MD5" ) ; } catch ( Exception ex ) { throw new IllegalStateException ( ex . getMessage ( ) ) ; } engineReset ( ) ; }
target:  Creates an HMACT64 instance which uses the given secret key material.