I'm having an issue where I had to modify a well-known nonce value used to AES-GCM encrypt a given cleartext in order to produce the expected ciphertext. More specifically, I had to increment the last byte of the 12-byte nonce value by 1 (or 2) in order to get the AES-GCM to produce the expected output.
RFC9001 specifies sample key and nonce values for QUIC protocol payload and header encryption/obfuscation. So one would assume using these sample values would be pretty straightforward. (https://www.rfc-editor.org/rfc/rfc9001.html#name-sample-packet-protection) For example:
key: 1f369613dd76d5467730efcbe3b1a22d (HKDF derived key) iv/nonce: fa044b2f42a3fd3b46fb255c (HKDF derived key) auth data: c300000001088394c8f03e5157080000449e00000002 (QUIC header in unprotected form) The problem is when an AES-GCM encryption function is used with these given parameters the ciphertext produced is not what is expected. When the last byte of the nonce is changed from x5c to x5e (i.e. incremented by 2) the output matches the one specified in the RFC. I had to increment it by 1 in another sample with a shorter plaintext.
I've tried many AES-GCM implementations and they all behave the same way. The original IV/nonce doesn't yield the expected output.
Please let me know if you have any idea what I'm missing here. Thanks!
(Below is a simple C# implementation for reference. Note that the last byte of the IV has already been incremented by 2 in order to get the correct output.
using System; using System.Security.Cryptography; namespace aes_gcm { class Program { static void Main(string[] args) { byte[] key = new byte[16] { 0x1f, 0x36, 0x96, 0x13, 0xdd, 0x76, 0xd5, 0x46, 0x77, 0x30, 0xef, 0xcb, 0xe3, 0xb1, 0xa2, 0x2d }; // rfc byte[] nonce = new byte[12] { 0xfa, 0x04, 0x4b, 0x2f, 0x42, 0xa3, 0xfd, 0x3b, 0x46, 0xfb, 0x25, 0x5e }; byte[] authData = new byte[] { 0xc3, 0x00, 0x00, 0x00, 0x01, 0x08, 0x83, 0x94, 0xc8, 0xf0, 0x3e, 0x51, 0x57, 0x08, 0x00, 0x00, 0x44, 0x9e, 0x00, 0x00, 0x00, 0x02 }; byte[] authTag = new byte[16]; byte[] client_init_payload = new byte[1162] { 0x06,0x00,0x40,0xf1,0x01,0x00,0x00,0xed,0x03,0x03,0xeb,0xf8,0xfa,0x56,0xf1,0x29, 0x39,0xb9,0x58,0x4a,0x38,0x96,0x47,0x2e,0xc4,0x0b,0xb8,0x63,0xcf,0xd3,0xe8,0x68, 0x04,0xfe,0x3a,0x47,0xf0,0x6a,0x2b,0x69,0x48,0x4c,0x00,0x00,0x04,0x13,0x01,0x13, 0x02,0x01,0x00,0x00,0xc0,0x00,0x00,0x00,0x10,0x00,0x0e,0x00,0x00,0x0b,0x65,0x78, 0x61,0x6d,0x70,0x6c,0x65,0x2e,0x63,0x6f,0x6d,0xff,0x01,0x00,0x01,0x00,0x00,0x0a, 0x00,0x08,0x00,0x06,0x00,0x1d,0x00,0x17,0x00,0x18,0x00,0x10,0x00,0x07,0x00,0x05, 0x04,0x61,0x6c,0x70,0x6e,0x00,0x05,0x00,0x05,0x01,0x00,0x00,0x00,0x00,0x00,0x33, 0x00,0x26,0x00,0x24,0x00,0x1d,0x00,0x20,0x93,0x70,0xb2,0xc9,0xca,0xa4,0x7f,0xba, 0xba,0xf4,0x55,0x9f,0xed,0xba,0x75,0x3d,0xe1,0x71,0xfa,0x71,0xf5,0x0f,0x1c,0xe1, 0x5d,0x43,0xe9,0x94,0xec,0x74,0xd7,0x48,0x00,0x2b,0x00,0x03,0x02,0x03,0x04,0x00, 0x0d,0x00,0x10,0x00,0x0e,0x04,0x03,0x05,0x03,0x06,0x03,0x02,0x03,0x08,0x04,0x08, 0x05,0x08,0x06,0x00,0x2d,0x00,0x02,0x01,0x01,0x00,0x1c,0x00,0x02,0x40,0x01,0x00, 0x39,0x00,0x32,0x04,0x08,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0x05,0x04,0x80, 0x00,0xff,0xff,0x07,0x04,0x80,0x00,0xff,0xff,0x08,0x01,0x10,0x01,0x04,0x80,0x00, 0x75,0x30,0x09,0x01,0x10,0x0f,0x08,0x83,0x94,0xc8,0xf0,0x3e,0x51,0x57,0x08,0x06, 0x04,0x80,0x00,0xff,0xff, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00 }; byte[] cipherBytes = new byte[client_init_payload.Length]; // perform encryption using (AesGcm aesgcm = new AesGcm(key, 16)) aesgcm.Encrypt(nonce, client_init_payload, cipherBytes, authTag, authData); } } } 
