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d4rp4t merged 2 commits into from
Jan 20, 2026
Merged

Chore/update p2bk #28

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9b64115
remove keysetid from p2bk derivation
d4rp4t Jan 18, 2026
978e77e
Adjust tests for new P2BK derivation
d4rp4t Jan 18, 2026
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109 changes: 54 additions & 55 deletions DotNut.Tests/UnitTest1.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -781,61 +781,60 @@ public void NullExpiryTests_PostMeltQuoteBolt11Response()
private static readonly byte[] P2BK_PREFIX = "Cashu_P2BK_v1"u8.ToArray();

[Fact]
public void Nut26Tests()
public void Nut28_P2BK_Tests()
{
// sender ephemeral keypair
var e = new PrivKey("1cedb9df0c6872188b560ace9e35fd55c2532d53e19ae65b46159073886482ca");
var E = new PubKey("02a8cda4cf448bfce9a9e46e588c06ea1780fcb94e3bbdf3277f42995d403a8b0c");

Assert.Equal(E.Key.ToString()?.ToLowerInvariant(), e.Key.CreatePubKey().ToString().ToLowerInvariant());
Assert.Equal(E.Key.ToString()?.ToLowerInvariant(), e.Key.CreatePubKey().ToString()?.ToLowerInvariant());

// receiver keypair
var p = new PrivKey("ad37e8abd800be3e8272b14045873f4353327eedeb702b72ddcc5c5adff5129c");
var P = new PubKey("02771fed6cb88aaac38b8b32104a942bf4b8f4696bc361171b3c7d06fa2ebddf06");

Assert.Equal(P.Key.ToString().ToLowerInvariant(), p.Key.CreatePubKey().ToString().ToLowerInvariant());
Assert.Equal(P.Key.ToString()?.ToLowerInvariant(), p.Key.CreatePubKey().ToString()?.ToLowerInvariant());

var kid = new KeysetId("009a1f293253e41e");
// var kid = new KeysetId("009a1f293253e41e");

var zx = "40d6ba4430a6dfa915bb441579b0f4dee032307434e9957a092bbca73151df8b";
Assert.Equal(zx, Convert.ToHexString(Cashu.ComputeZx(e, P)).ToLowerInvariant());
Assert.Equal(zx, Convert.ToHexString(Cashu.ComputeZx(p, E)).ToLowerInvariant());

string[] rs =
[
"41b5f15975f787bd5bd8d91753cbbe56d0d7aface851b1063e8011f68551862d",
"c4d68c79b8676841f767bcd53437af3f43d51b205f351d5cdfe5cb866ec41494",
"04ecf53095882f28965f267e46d2c555f15bcd74c3a84f42cf0de8ebfb712c7c",
"4163bc31b3087901b8b28249213b0ecc447cee3ea1f0c04e4dd5934e0c3f78ad",
"f5d6d20c399887f29bdda771660f87226e3a0d4ef36a90f40d3f717085957b60",
"f275404a115cd720ee099f5d6b7d5dc705d1c95ac6ae01c917031b64f7dccc72",
"39dffa9f0160bcda63920305fc12f88d824f5b654970dbd579c08367c12fcd78",
"3331338e87608c7f36265c9b52bb5ebeac1bb3e2220d2682370f4b7c09dccd4b",
"44947bd36c0200fb5d5d05187861364f6b666aac8ce37b368e27f01cea7cf147",
"cf4e69842833e0dab8a7302933d648fee98de80284af2d7ead71b420a8f0ebde",
"3638eae8a9889bbd96769637526010b34cd1e121805eaaaaa0602405529ca92f"
"f43cfecf4d44e109872ed601156a01211c0d9eba0460d5be254a510782a2d4aa",
"4a57e6acb9db19344af5632aa45000cd2c643550bc63c7d5732221171ab0f5b3",
"d4a8b84b21f2b0ad31654e96eddbc32bfdedae2d05dc179bdd6cc20236b1104d",
"ecebf43123d1da3de611a05f5020085d63ca20829242cdc07f7c780e19594798",
"5f42d463ead44cbb20e51843d9eb3b8b0e0021566fd89852d23ae85f57d60858",
"a8f1c9d336954997ad571e5a5b59fe340c80902b10b9099d44e17abb3070118c",
"c39fa43b707215c163593fb8cadc0eddb4fe2f82c0c79c82a6fc2e3b6b051a7e",
"b17d6a51396eb926f4a901e20ff760a852563f90fd4b85e193888f34fd2ee523",
"4d4af85ea296457155b7ce328cf9accbe232e8ac23a1dfe901a36ab1b72ea04d",
"ce311248ea9f42a73fc874b3ce351d55964652840d695382f0018b36bb089dd1",
"9de35112d62e6343d02301d8f58fef87958e99bb68cfdfa855e04fe18b95b114",
];

for (int i = 0; i <= 10; i++)
{
var ri = (PrivKey)Cashu.ComputeRi(Convert.FromHexString(zx), kid.GetBytes(), i);
var ri = (PrivKey)Cashu.ComputeRi(Convert.FromHexString(zx), i);
Assert.Equal(rs[i], ri.ToString());
}


string[] blindedPublicKeys =
[
"03f221b62aa21ee45982d14505de2b582716ae95c265168f586dc547f0ea8f135f",
"0299692178029fe08c49e8123bb0e84d6e960b27f82c8aed43013526489d46c0d5",
"03ae189850bda004f9723e17372c99ff9df9e29750d2147d40efb45ac8ab2cdd2c",
"03109838d718fbe02e9458ffa423f25bae0388146542534f8e2a094de6f7b697fa",
"0339d5ed7ea93292e60a4211b2daf20dff53f050835614643a43edccc35c8313db",
"0237861efcd52fe959bce07c33b5607aeae0929749b8339f68ba4365f2fb5d2d8d",
"026d5500988a62cde23096047db61e9fb5ef2fea5c521019e23862108ea4e14d72",
"039024fd20b26e73143509537d7c18595cfd101da4b18bb86ddd30e944aac6ef1b",
"03017ec4218ca2ed0fbe050e3f1a91221407bf8c896b803a891c3a52d162867ef8",
"0380dc0d2c79249e47b5afb61b7d40e37b9b0370ec7c80b50c62111021b886ab31",
"0261a8a32e718f5f27610a2b7c2069d6bab05d1ead7da21aa9dd2a3c758bdf6479"
"03b7c03eb05a0a539cfc438e81bcf38b65b7bb8685e8790f9b853bfe3d77ad5315",
"0352fb6d93360b7c2538eedf3c861f32ea5883fceec9f3e573d9d84377420da838",
"03667361ca925065dcafea0a705ba49e75bdd7975751fcc933e05953463c79fff1",
"02aca3ed09382151250b38c85087ae0a1436a057b40f824a5569ba353d40347d08",
"02cd397bd6e326677128f1b0e5f1d745ad89b933b1b8671e947592778c9fc2301d",
"0394140369aae01dbaf74977ccbb09b3a9cf2252c274c791ac734a331716f1f7d4",
"03480f28e8f8775d56a4254c7e0dfdd5a6ecd6318c757fcec9e84c1b48ada0666d",
"02f8a7be813f7ba2253d09705cc68c703a9fd785a055bf8766057fc6695ec80efc",
"03aa5446aaf07ca9730b233f5c404fd024ef92e3787cd1c34c81c0778fe23c59e9",
"037f82d4e0a79b0624a58ef7181344b95afad8acf4275dad49bcd39c189b73ece2",
"032371fc0eef6885062581a3852494e2eab8f384b7dd196281b85b77f94770fac5",
];
//it's the same blinding as with computeB_
for (int i = 0; i <= 10; i++)
Expand All @@ -845,45 +844,45 @@ public void Nut26Tests()

string[] skStd =
[
"eeedda054df845fbde4b8a579952fd9a240a2e9ad3c1dc791c4c6e51654698c9",
"720e75259068268079da6e1579beee83dc58bd279b5ca893fddfc9547e82e5ef",
"b224dddc6d88ed6718d1d7be8c5a0499448e4c62af187ab5acda4546db663f18",
"ee9ba4dd8b0937403b25338966c24e0f97af6d2c8d60ebc12ba1efa8ec348b49",
"a30ebab8119946311e5058b1ab96c66706bdaf562f921c2b2b396f3e95544cbb",
"9fad28f5e95d955f707c509db1049d0b9e556b6202d58d0034fd1933079b9dcd",
"e717e34ad9617b18e604b446419a37d0d581da5334e10748578cdfc2a124e014",
"e0691c3a5f614abdb8990ddb98429e01ff4e32d00d7d51f514dba7d6e9d1dfe7",
"f1cc647f4402bf39dfcfb658bde87592be98e99a7853a6a96bf44c77ca7203e3",
"7c86523000349f193b19e169795d884382118a09c0d6b8b5cb6bb1eeb8afbd39",
"e370d394818959fc18e9477797e74ff6a004600f6bced61d7e2c80603291bbcb"
"a174e77b25459f4809a187415af14065b49140c1408860f543444ed59261a605",
"f78fcf5891dbd772cd68146ae9d740107f96b43ea7d3f34850ee7d71faa6084f",
"81e0a0f6f9f36eebb3d7ffd733630270967150344203a2d2fb66bfd0466fe1a8",
"9a23dcdcfbd2987c6884519f95a747a1fc4dc289ce6a58f79d7675dc291818f3",
"0c7abd0fc2d50af9a357c9841f727acfa683c35dac002389f034e62d6794d9b3",
"5629b27f0e9607d62fc9cf9aa0e13d78a50432324ce094d462db7889402ee2e7",
"70d78ce74872d3ffe5cbf0f910634e224d81d189fcef27b9c4f62c097ac3ebd9",
"5eb552fd116f7765771bb322557e9fecead9e19839731118b1828d030cedb67e",
"fa82e10a7a9703afd82a7f72d280ec0f3565679a0f120b5bdf6fc70c9723b2e9",
"7b68faf4c2a000e5c23b25f413bc5c9a2ec9f48b4990deba0dfb8904cac76f2c",
"4b1b39beae2f21825295b3193b172ecc2e123bc2a4f76adf73da4daf9b54826f",
];

for (int i = 0; i <= 10; i++)
{
var ri = Cashu.ComputeRi(Convert.FromHexString(zx), kid.GetBytes(), i);
var ri = Cashu.ComputeRi(Convert.FromHexString(zx), i);
var derivedKey = p.Key.TweakAdd(ri.ToBytes());

Assert.Equal(skStd[i], Convert.ToHexString(derivedKey.ToBytes()).ToLowerInvariant());
}

string[] skNeg =
[
"947e08ad9df6c97ed96627d70e447f1238540da5ac2a25cf208614287592b4d2",
"179ea3cde066aa0374f50b94eeb06ffbf0a29c3273c4f1ea02196f2b8ecf01f8",
"57b50c84bd8770ea13ec753e014b861158d82b6d8780c40bb113eb1debb25b21",
"942bd385db07bac3363fd108dbb3cf87abf94c3765c935172fdb957ffc80a752",
"489ee9606197c9b4196af631208847df1b078e6107fa65812f731515a5a068c4",
"453d579e395c18e26b96ee1d25f61e83b29f4a6cdb3dd6563936bf0a17e7b9d6",
"8ca811f3295ffe9be11f51c5b68bb948e9cbb95e0d49509e5bc68599b170fc1d",
"85f94ae2af5fce40b3b3ab5b0d341f7a139811dae5e59b4b19154dadfa1dfbf0",
"975c9327940142bcdaea53d832d9f70ad2e2c8a550bbefff702df24edabe1fec",
"221680d85033229c36347ee8ee4f09bb965b6914993f020bcfa557c5c8fbd942",
"8901023cd187dd7f1403e4f70cd8d16eb44e3f1a44371f738266263742ddd7d4",
"47051623754422cb04bc24c0cfe2c1ddc8db1fcc18f0aa4b477df4aca2adc20e",
"9d1ffe00e1da5af5c882b1ea5ec8c18893e09349803c3c9e552823490af22458",
"2770cf9f49f1f26eaef29d56a85483e8aabb2f3f1a6bec28ffa065a756bbfdb1",
"3fb40b854bd11bff639eef1f0a98c91a1097a194a6d2a24da1b01bb3396434fc",
"b20aebb812d38e7c9e7267039463fc46757c7f4f33b10d1bb440ea91481736fd",
"fbb9e1275e948b592ae46d1a15d2beef73fcee23d4917e6626e77ced20b14031",
"1667bb8f98715782e0e68e788554cf9a61cbb094d557710fc92fd1e08b1007e2",
"044581a5616dfae8723650a1ca702164ff23c0a311db5a6eb5bc32da1d39d287",
"a0130fb2ca958732d3451cf247726d8749af46a4e77a54b1e3a96ce3a76fcef2",
"20f9299d129e8468bd55c37388adde124313d39621f9281012352edbdb138b35",
"f0ab6866fe2da5054db05098b008b042fd0af7b42ca8547137e652137bd6dfb9"
];

for (int i = 0; i <= 10; i++)
{
var ri = Cashu.ComputeRi(Convert.FromHexString(zx), kid.GetBytes(), i);
var ri = Cashu.ComputeRi(Convert.FromHexString(zx), i);
var derivedKeyNeg = p.Key.sec.Negate().Add(ri.sec).ToPrivateKey();

Assert.Equal(skNeg[i], Convert.ToHexString(derivedKeyNeg.ToBytes()).ToLowerInvariant());
Expand All @@ -892,7 +891,7 @@ public void Nut26Tests()
}

[Fact]
public void Nut26_Flow()
public void Nut28_P2BK_Flow()
{
// sender generates ephermal keypair
var e = new PrivKey("1cedb9df0c6872188b560ace9e35fd55c2532d53e19ae65b46159073886482ca");
Expand All @@ -918,7 +917,7 @@ public void Nut26_Flow()
SignatureThreshold = 2,
SigFlag = "SIG_INPUTS"
};
var p2pkProofSecret = conditions.BuildBlinded(keysetId, e);
var p2pkProofSecret = conditions.BuildBlinded(e);

var secret = new Nut10Secret(P2PKProofSecret.Key, p2pkProofSecret);

Expand Down Expand Up @@ -956,7 +955,7 @@ public void Nut26_Flow_WithRandomE()
SignatureThreshold = 2,
SigFlag = "SIG_INPUTS"
};
var p2pkProofSecret = conditions.BuildBlinded(keysetId, out var E);
var p2pkProofSecret = conditions.BuildBlinded(out var E);

var secret = new Nut10Secret(P2PKProofSecret.Key, p2pkProofSecret);

Expand Down
15 changes: 6 additions & 9 deletions DotNut/Cashu.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -134,23 +134,20 @@ public static ECPubKey ComputeC(ECPubKey C_, ECPrivKey r, ECPubKey A)
public static byte[] ComputeZx(ECPrivKey e, ECPubKey P)
{
var x = (e.sec * P.Q).ToGroupElement().x;
if (!ECXOnlyPubKey.TryCreate(x, Context.Instance, out var xOnly))
{
// should never happen
throw new InvalidOperationException("Could not create xOnly pubkey");
}
return xOnly.ToBytes();
return ECXOnlyPubKey.TryCreate(x, Context.Instance, out var xOnly)
? xOnly.ToBytes()
: throw new InvalidOperationException("Could not create xOnly pubkey");
}

public static ECPrivKey ComputeRi(byte[] Zx, byte[] keysetId, int i)
public static ECPrivKey ComputeRi(byte[] Zx, int i)
{
byte[] hash;

hash = SHA256.HashData(Concat(P2BK_PREFIX, Zx, keysetId, [(byte)(i & 0xFF)]));
hash = SHA256.HashData(Concat(P2BK_PREFIX, Zx, [(byte)(i & 0xFF)]));
var hashValue = new BigInteger(hash);
if (hashValue == 0 || hashValue.CompareTo(N) != -1)
{
hash = SHA256.HashData(Concat(P2BK_PREFIX, Zx, keysetId, [(byte)(i & 0xFF)], [0xff]));
hash = SHA256.HashData(Concat(P2BK_PREFIX, Zx, [(byte)(i & 0xFF)], [0xff]));
}
return ECPrivKey.Create(hash);
}
Expand Down
15 changes: 5 additions & 10 deletions DotNut/P2PKBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -132,28 +132,23 @@ private void Validate()
*/

//For sig_inputs, generates random p2pk_e for each input
public P2PKProofSecret BuildBlinded(KeysetId keysetId, out ECPubKey p2pkE)
public P2PKProofSecret BuildBlinded(out ECPubKey p2pkE)
{
var e = new PrivKey(RandomNumberGenerator.GetHexString(64));
p2pkE = e.Key.CreatePubKey();
return BuildBlinded(keysetId, e);
return BuildBlinded(e);
}

//For sig_all, p2pk_e must be provided
public P2PKProofSecret BuildBlinded(KeysetId keysetId, ECPrivKey p2pke)
public P2PKProofSecret BuildBlinded(ECPrivKey p2pke)
{
var pubkeys = RefundPubkeys != null ? Pubkeys.Concat(RefundPubkeys).ToArray() : Pubkeys;
var rs = new List<ECPrivKey>();
bool extraByte = false;

var keysetIdBytes = keysetId.GetBytes();

var e = p2pke;

for (int i = 0; i < pubkeys.Length; i++)
{
var Zx = Cashu.ComputeZx(e, pubkeys[i]);
var Ri = Cashu.ComputeRi(Zx, keysetIdBytes, i);
var Zx = Cashu.ComputeZx(p2pke, pubkeys[i]);
var Ri = Cashu.ComputeRi(Zx, i);
rs.Add(Ri);
}
_blindPubkeys(rs.ToArray());
Expand Down
9 changes: 4 additions & 5 deletions DotNut/P2PKProofSecret.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -154,15 +154,15 @@ public virtual ECPubKey[] GetAllowedRefundPubkeys(out int? requiredSignatures)
if (requiredRefundSignatures == 0)
return null;

var (isValid, result) = TrySignBlindPath(allowedKeys.ToArray(), requiredSignatures, keys, keysetId, P2PkE, msg);
var (isValid, result) = TrySignBlindPath(allowedKeys.ToArray(), requiredSignatures, keys, P2PkE, msg);
if (isValid)
{
return result;
}

if (requiredRefundSignatures.HasValue && allowedRefundKeys.Any())
{
(isValid, result) = TrySignBlindPath(allowedRefundKeys.ToArray(), requiredRefundSignatures.Value, keys, keysetId, P2PkE, msg);
(isValid, result) = TrySignBlindPath(allowedRefundKeys.ToArray(), requiredRefundSignatures.Value, keys, P2PkE, msg);
if (isValid)
{
return result;
Expand All @@ -174,11 +174,10 @@ public virtual ECPubKey[] GetAllowedRefundPubkeys(out int? requiredSignatures)


private (bool IsValid, P2PKWitness Witness) TrySignBlindPath(ECPubKey[] allowedKeys, int requiredSignatures,
ECPrivKey[] availableKeys, KeysetId keysetId, ECPubKey P2PkE, byte[] msg)
ECPrivKey[] availableKeys, ECPubKey P2PkE, byte[] msg)
{
var allowedKeysSet = new HashSet<ECPubKey>(allowedKeys);
var result = new P2PKWitness();
var keysetIdBytes = keysetId.GetBytes();
var usedSlots = new HashSet<int>();

foreach (var key in availableKeys)
Expand All @@ -191,7 +190,7 @@ public virtual ECPubKey[] GetAllowedRefundPubkeys(out int? requiredSignatures)
if (usedSlots.Contains(i)) continue;

var Zx = Cashu.ComputeZx(key, P2PkE);
var ri = Cashu.ComputeRi(Zx, keysetIdBytes, i);
var ri = Cashu.ComputeRi(Zx, i);
var tweakedPrivkey = key.TweakAdd(ri.ToBytes());
var tweakedPubkey = tweakedPrivkey.CreatePubKey();

Expand Down