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Skip hypertree root recomputation when signing SLH-DSA #195

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Merged
Xor-el merged 1 commit into from
Sep 1, 2026
+13 −19
Merged

Skip hypertree root recomputation when signing SLH-DSA #195

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2 changes: 1 addition & 1 deletion CryptoLib/src/Crypto/Generators/ClpSlhDsaGenerators.pas
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Original file line number Diff line number Diff line change
Expand Up @@ -78,7 +78,7 @@ function TSlhDsaKeyPairGenerator.GenerateKeyPair: IAsymmetricCipherKeyPair;
LHt := TSlhDsaHT.Create(LEngine, LSk.Seed, LPkSeed);
try
LPk.Seed := LPkSeed;
LPk.Root := LHt.GetHTPubKey;
LPk.Root := LHt.PKGen;
finally
LHt.Free;
end;
Expand Down
30 changes: 12 additions & 18 deletions CryptoLib/src/Crypto/Signers/SlhDsa/ClpSlhDsaCore.pas
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Expand Up @@ -154,7 +154,6 @@ TSlhDsaHT = class
FPkSeed: TCryptoLibByteArray;
FEngine: ISlhDsaEngine;
FWots: TSlhDsaWotsPlus;
FHTPubKey: TCryptoLibByteArray;
class function GetXmssOffset(const AEngine: ISlhDsaEngine): Int32; static;
function XmssPkFromSig(AIdx: UInt32; const ASigXmss: TCryptoLibByteArray; ASigXmssOff: Int32;
const AM, APkSeed: TCryptoLibByteArray; const AParamAdrs: ISlhDsaAdrs): TCryptoLibByteArray;
Expand All @@ -165,7 +164,9 @@ TSlhDsaHT = class
public
constructor Create(const AEngine: ISlhDsaEngine; const ASkSeed, APkSeed: TCryptoLibByteArray);
destructor Destroy; override;
function GetHTPubKey: TCryptoLibByteArray;
// Computes PK.root; only key generation calls this. Signing already holds
// PK.root, so recomputing here would cost a full top-layer XMSS tree build.
function PKGen: TCryptoLibByteArray;
procedure Sign(const AM: TCryptoLibByteArray; AIdxTree: UInt64; AIdxLeaf: UInt32;
var ASignature: TCryptoLibByteArray);
function Verify(const AM, ASignature, APkSeed: TCryptoLibByteArray; AIdxTree: UInt64; AIdxLeaf: UInt32;
Expand Down Expand Up @@ -653,26 +654,12 @@ procedure TSlhDsaWotsPlus.PKFromSig(const ASig: TCryptoLibByteArray; ASigOff: In
{ TSlhDsaHT }

constructor TSlhDsaHT.Create(const AEngine: ISlhDsaEngine; const ASkSeed, APkSeed: TCryptoLibByteArray);
var
LAdrs: ISlhDsaAdrs;
begin
inherited Create;
FSkSeed := ASkSeed;
FPkSeed := APkSeed;
FEngine := AEngine;
FWots := TSlhDsaWotsPlus.Create(AEngine);

LAdrs := TSlhDsaAdrs.Create;
LAdrs.SetLayerAddress(UInt32(FEngine.D - 1));
LAdrs.SetTreeAddress(0);

if ASkSeed <> nil then
begin
System.SetLength(FHTPubKey, FEngine.N);
TreeHash(ASkSeed, 0, FEngine.HPrime, APkSeed, LAdrs, FHTPubKey, 0);
end
else
FHTPubKey := nil;
end;

destructor TSlhDsaHT.Destroy;
Expand All @@ -682,9 +669,16 @@ destructor TSlhDsaHT.Destroy;
inherited Destroy;
end;

function TSlhDsaHT.GetHTPubKey: TCryptoLibByteArray;
function TSlhDsaHT.PKGen: TCryptoLibByteArray;
var
LAdrs: ISlhDsaAdrs;
begin
Result := FHTPubKey;
LAdrs := TSlhDsaAdrs.Create;
LAdrs.SetLayerAddress(UInt32(FEngine.D - 1));
LAdrs.SetTreeAddress(0);

System.SetLength(Result, FEngine.N);
TreeHash(FSkSeed, 0, FEngine.HPrime, FPkSeed, LAdrs, Result, 0);
end;

class function TSlhDsaHT.GetXmssOffset(const AEngine: ISlhDsaEngine): Int32;
Expand Down
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