Jon Chery
dee6d88d87
---ci--- project: acdl phase: 4 milestone: v1.28 status: execute persona: security-engineer ---
53 lines
2.0 KiB
Markdown
53 lines
2.0 KiB
Markdown
# KMS asymmetric key provisioning (C-1.1)
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This document records the C-1.1 verification for the Nova OIDC signing
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KMS key and the provisioning path used by `nova idp setup`.
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## C-1.1 verification (P4)
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C-1.1 requires verifying KMS asymmetric key support **before**
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implementation. The verification command is:
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```
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aws kms create-key \
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--key-spec ECC_NIST_P256 \
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--key-usage SIGN_VERIFY \
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--description nova-oidc-signing
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```
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**Result on the P4 build host:** AWS credentials are not available
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(`Unable to locate credentials`), so the live verification could not
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run. This is recorded as a **P4 CI gate**: the `nova idp setup --check`
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command (Wave 8) performs this verification when AWS creds are present
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and reports it as a missing prerequisite when they are not. The code
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proceeds against the documented KMS API (REQ-337); tests use a test
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ECDSA P-256 keypair + mocked `boto3.client("kms")` (no real AWS calls).
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KMS asymmetric signing keys (`ECC_NIST_P256` + `SIGN_VERIFY`) are GA
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in all commercial regions (announced 2020-11). The
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`ECDSA_SHA_256` signing algorithm is supported. Confidence: high.
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## Key spec (REQ-337)
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* **Key spec:** `ECC_NIST_P256` (NIST P-256 / secp256r1)
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* **Key usage:** `SIGN_VERIFY`
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* **Signing algorithm:** `ECDSA_SHA_256` (JWS `ES256`)
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* **Alias:** `alias/nova-oidc-signing`
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* **Rotation:** manual, 90 days (matches D-069 CMK cadence). New key +
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re-point alias + JWKS serves both `kid`s during overlap.
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## DER → raw ECDSA conversion (the #1 gotcha)
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KMS `sign()` returns a **DER-encoded** ASN.1 ECDSA signature. JWS
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(RFC 7515 §3.1.3) requires the **raw** `r‖s` concatenation, each
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coordinate 32 bytes big-endian. The conversion (in
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`core/kms_signing.py:der_to_raw_ecdsa`):
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```python
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from cryptography.hazmat.primitives.asymmetric.utils import decode_dss_signature
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r, s = decode_dss_signature(der_sig)
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raw = r.to_bytes(32, "big") + s.to_bytes(32, "big")
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```
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This is verified by `tests/test_kms_signing.py` and the CAP-037
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round-trip test (`tests/test_kms_roundtrip.py`). |