fix: use random nonce per call in AES-GCM onboarding signature#270
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Replaces the static IV (first 12 bytes of the secret) with OpenSSL::Random.random_bytes(12) generated fresh for every encryption call. The old approach caused AES-GCM nonce reuse: an attacker who collects two onboarding_signature values from partner URLs can XOR the ciphertexts to cancel the keystream and forge a valid signature for any submerchant ID without knowing the partner secret key (NIST SP 800-38D §8.3 Forbidden Attack). New output format: hex(iv[12] || ciphertext || tag[16]) The receiver reads the first 24 hex chars as the IV before decrypting. Reported via HackerOne #3754503 (ISS-2528895), SLA: 2026-06-05. Co-authored-by: ankitdas13 <ankit.das@razorpay.com>
This was referenced Jun 9, 2026
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Summary
generate_onboarding_signatureto use a random 12-byte IV per encryption call instead of a static IV.hex(iv[12 bytes] || ciphertext || tag[16 bytes])Changes
Companion PRs (same fix across all partner SDKs)
Test plan
generate_onboarding_signatureproduces a different hex string on every call with the same input🤖 Generated with Claude Code