Connecting to KMS endpoint with s2nc by using PQ-ciphers

[cschnidr]

For testing/demo purposes I'm trying to connect to a KMS endpoint and enforcing PQ-ciphers.
I compiled AWS-LC and S2N-TLS from the source as described here: https://repost.aws/questions/QU882YiZEHTRe1GTyxKr99Xg/building-s2n-tls-with-aws-libcrypto-with-pq-support

However, I don't find a cipher suite that uses TLS1.3 and PQ-Ciphers. What I'm doing wrong? What security policy is recommended?

Here the closest I got:

[ec2-user@ip-172-31-0-117 bin]$ ./s2nc -c KMS-PQ-TLS-1-0-2020-07 kms.eu-central-2.amazonaws.com
CONNECTED:
Handshake: NEGOTIATED|FULL_HANDSHAKE|TLS12_PERFECT_FORWARD_SECRECY
Client hello version: 33
Client protocol version: 33
Server protocol version: 33
Actual protocol version: 33
Server name: kms.eu-central-2.amazonaws.com
Curve: secp256r1
KEM: kyber512r3
KEM Group: NONE
Cipher negotiated: ECDHE-KYBER-RSA-AES256-GCM-SHA384
Server signature negotiated: RSA+SHA256
Early Data status: NOT REQUESTED
Wire bytes in: 6565
Wire bytes out: 1099
s2n is ready
Connected to kms.eu-central-2.amazonaws.com:443

--> TLS1.2, Cipher negotiated: ECDHE-KYBER-RSA-AES256-GCM-SHA384
--> no KEM Group?

[ec2-user@ip-172-31-0-117 bin]$ ./s2nc -c PQ-TLS-1-0-2021-05-23 kms.eu-central-2.amazonaws.com
CONNECTED:
Handshake: NEGOTIATED|FULL_HANDSHAKE|MIDDLEBOX_COMPAT
Client hello version: 33
Client protocol version: 34
Server protocol version: 34
Actual protocol version: 34
Server name: kms.eu-central-2.amazonaws.com
Curve: NONE
KEM: NONE
KEM Group: x25519_kyber-512-r3
Cipher negotiated: TLS_AES_256_GCM_SHA384
Server signature negotiated: RSA-PSS-RSAE+SHA256
Early Data status: NOT REQUESTED
Wire bytes in: 6586
Wire bytes out: 1224
s2n is ready
Connected to kms.eu-central-2.amazonaws.com:443

--> TLS1.3, KEM Group: x25519_kyber-512-r3
--> no KEM? One choosen from the group?
--> Cipher negotiated: TLS_AES_256_GCM_SHA384

[lrstewart]

Looking at your output: it looks like you're successfully using PQ key exchange. "KEM" is for TLS1.2, and "KEM group" is for TLS1.3. They're two different mechanisms. PQ key exchange in TLS1.3 doesn't involve a specific cipher suite, because key exchange is separate from cipher suite in TLS1.3.

[cschnidr]

Makes sense! Missed this. For reference a slightly longer explanation: https://repost.aws/questions/QU882YiZEHTRe1GTyxKr99Xg/building-s2n-tls-with-aws-libcrypto-with-pq-support