Watson Ladd has pointed out that since breaking authentication 10 years after it's been deprecated does not let you retroactively MITM someone but breaking key

Watson Ladd has pointed out that since breaking authentication 10 years after it's been deprecated does not let you retroactively MITM someone but breaking key exchange 10 years after it's been deprecated allows decryption of stored intercepts, KEX should be stronger than certificates. So make sure your TLS server with 1024 bit key uses ECDHE or 2048 bit DHE, not plain RSA KEX.