diff options
Diffstat (limited to 'crypto/src/math/ec/rfc8032/Scalar25519.cs')
| -rw-r--r-- | crypto/src/math/ec/rfc8032/Scalar25519.cs | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/crypto/src/math/ec/rfc8032/Scalar25519.cs b/crypto/src/math/ec/rfc8032/Scalar25519.cs index 4fb2fd2da..08ab80607 100644 --- a/crypto/src/math/ec/rfc8032/Scalar25519.cs +++ b/crypto/src/math/ec/rfc8032/Scalar25519.cs @@ -595,7 +595,7 @@ namespace Org.BouncyCastle.Math.EC.Rfc8032 #endif #if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER - internal static void ReduceBasisVar(ReadOnlySpan<uint> k, Span<uint> z0, Span<uint> z1) + internal static bool ReduceBasisVar(ReadOnlySpan<uint> k, Span<uint> z0, Span<uint> z1) { /* * Split scalar k into two half-size scalars z0 and z1, such that z1 * k == z0 mod L. @@ -612,11 +612,16 @@ namespace Org.BouncyCastle.Math.EC.Rfc8032 Span<uint> v0 = stackalloc uint[4]; v0.CopyFrom(k); Span<uint> v1 = stackalloc uint[4]; v1[0] = 1U; + // Conservative upper bound on the number of loop iterations needed + int iterations = TargetLength * 4; int last = 15; int len_Nv = ScalarUtilities.GetBitLengthPositive(last, Nv); while (len_Nv > TargetLength) { + if (--iterations < 0) + return false; + int len_p = ScalarUtilities.GetBitLength(last, p); int s = len_p - len_Nv; s &= ~(s >> 31); @@ -646,9 +651,10 @@ namespace Org.BouncyCastle.Math.EC.Rfc8032 // v1 * k == v0 mod L v0.CopyTo(z0); v1.CopyTo(z1); + return true; } #else - internal static void ReduceBasisVar(uint[] k, uint[] z0, uint[] z1) + internal static bool ReduceBasisVar(uint[] k, uint[] z0, uint[] z1) { /* * Split scalar k into two half-size scalars z0 and z1, such that z1 * k == z0 mod L. @@ -665,11 +671,16 @@ namespace Org.BouncyCastle.Math.EC.Rfc8032 uint[] v0 = new uint[4]; Array.Copy(k, v0, 4); uint[] v1 = new uint[4]; v1[0] = 1U; + // Conservative upper bound on the number of loop iterations needed + int iterations = TargetLength * 4; int last = 15; int len_Nv = ScalarUtilities.GetBitLengthPositive(last, Nv); while (len_Nv > TargetLength) { + if (--iterations < 0) + return false; + int len_p = ScalarUtilities.GetBitLength(last, p); int s = len_p - len_Nv; s &= ~(s >> 31); @@ -699,6 +710,7 @@ namespace Org.BouncyCastle.Math.EC.Rfc8032 // v1 * k == v0 mod L Array.Copy(v0, z0, 4); Array.Copy(v1, z1, 4); + return true; } #endif |