How do I choose constants suitable for Diffe-Hellman?

-----BEGIN PGP SIGNED MESSAGE----- How do I choose constants suitable for Diffe-Hellman? According to _Applied Cryptography_ n should be prime, also (n-1)/2 should also be prime. g should be a primitive root of unity mod n. n should be 512 or 1024 bits long. Are there any other requirements? How can I choose such numbers? Are such numbers published anywhere? -----BEGIN PGP SIGNATURE----- Version: 2.6 iQCVAgUBLmNv5g2Gnhl89QSNAQEnOQQAq8N8NyL9aTFEFq7BfhmXp4J/K8cSiIZU pP+yaIymt69Ne4fqxv2R26wqgRtqSw/jENgmCOJpK1SIeqeRX0/X4WikAh/v+4uC UhvJ48aBiS5Yosct6I2NiFMINS91m0IoCicqNU2IyRG8mzSSzKUWvSivIGSy87VR 8LPgC/AvH8Q= =iDBs -----END PGP SIGNATURE-----