Skip to content

[GCM] Fix auth tag generation for large data #51

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Dec 29, 2022
Merged

[GCM] Fix auth tag generation for large data #51

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
af94b8b
Extract test logic for a single data set from TestTDECGCM.TestEncodeS…
denovosoftware Dec 21, 2022
33e397c
Add new test case TestTDECGCM.TestEncodeLargeStream to verify that ch…
denovosoftware Dec 21, 2022
283047b
Address out-of-bounds read issue in TGCM by explicitly specifying cip…
denovosoftware Dec 21, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
26 changes: 16 additions & 10 deletions Source/DECCipherModesGCM.pas
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -232,10 +232,14 @@ TGCM = class(TObject)
/// <param name="Ciphertext">
/// Encrypted data used in the calculation
/// </param>
/// <param name="CiphertextSize">
/// Length of the ciphertext in bytes. Use when reading part of array.
/// </param>
/// <returns>
/// Calculated raw hash value which will later get returned as AuthenticatedTag
/// </returns>
function CalcGaloisHash(AuthenticatedData, Ciphertext: TBytes): T128;
function CalcGaloisHash(AuthenticatedData, Ciphertext : TBytes; CiphertextSize:
Integer): T128;

/// <summary>
/// Encrypts a T128 value using the encryption method specified on init
Expand Down Expand Up @@ -518,23 +522,24 @@ procedure TGCM.Init(EncryptionMethod : TEncodeDecodeMethod;
b^ := 1;
end
else
FY := CalcGaloisHash(nil, InitVector);
FY := CalcGaloisHash(nil, InitVector, length(InitVector));

FEncryptionMethod(@FY[0], @FE_K_Y0[0], 16);
end;

function TGCM.CalcGaloisHash(AuthenticatedData, Ciphertext : TBytes): T128;
function TGCM.CalcGaloisHash(AuthenticatedData, Ciphertext : TBytes;
CiphertextSize: Integer): T128;
var
AuthCipherLength : T128;
x : T128;
n : Uint64;

procedure encode(data : TBytes);
procedure encode(data : TBytes; dataSize: Integer);
var
i, mod_d, div_d, len_d : UInt64;
hdata : T128;
begin
len_d := length(data);
len_d := dataSize;
if (len_d > 0) then
begin
n := 0;
Expand Down Expand Up @@ -565,9 +570,10 @@ function TGCM.CalcGaloisHash(AuthenticatedData, Ciphertext : TBytes): T128;

begin
x := nullbytes;
encode(AuthenticatedData);
encode(Ciphertext);
SetAuthenticationCipherLength(AuthCipherLength, length(AuthenticatedData) shl 3, length(ciphertext) shl 3);
encode(AuthenticatedData, length(AuthenticatedData));
Assert(length(Ciphertext) >= CiphertextSize);
encode(Ciphertext, CiphertextSize);
SetAuthenticationCipherLength(AuthCipherLength, length(AuthenticatedData) shl 3, CiphertextSize shl 3);

Result := poly_mult_H(XOR_T128(AuthCipherLength, x));
end;
Expand Down Expand Up @@ -598,7 +604,7 @@ procedure TGCM.DecodeGCM(Source, Dest: TBytes; Size: Integer);
XOR_ArrayWithT128(Source, i, UInt64(Size)-i, EncodeT128(FY), Dest);
end;

a_tag := XOR_T128(CalcGaloisHash(DataToAuthenticate, Source), FE_K_Y0);
a_tag := XOR_T128(CalcGaloisHash(DataToAuthenticate, Source, Size), FE_K_Y0);

Setlength(FCalcAuthenticationTag, FCalcAuthenticationTagLength);
Move(a_tag[0], FCalcAuthenticationTag[0], FCalcAuthenticationTagLength);
Expand Down Expand Up @@ -642,7 +648,7 @@ procedure TGCM.EncodeGCM(Source, Dest: TBytes; Size: Integer);
XOR_ArrayWithT128(Source, i, UInt64(Size)-i, EncodeT128(FY), Dest);
end;

AuthTag := XOR_T128(CalcGaloisHash(DataToAuthenticate, Dest), FE_K_Y0);
AuthTag := XOR_T128(CalcGaloisHash(DataToAuthenticate, Dest, Size), FE_K_Y0);
Setlength(FCalcAuthenticationTag, FCalcAuthenticationTagLength);
Move(AuthTag[0], FCalcAuthenticationTag[0], FCalcAuthenticationTagLength);
end;
Expand Down
Loading