diff --git a/crypto/src/crypto/engines/RSABlindedEngine.cs b/crypto/src/crypto/engines/RSABlindedEngine.cs
index d207f617c..8bb9a4f8c 100644
--- a/crypto/src/crypto/engines/RSABlindedEngine.cs
+++ b/crypto/src/crypto/engines/RSABlindedEngine.cs
@@ -110,31 +110,25 @@ namespace Org.BouncyCastle.Crypto.Engines
throw new InvalidOperationException("RSA engine not initialised");
BigInteger input = core.ConvertInput(inBuf, inOff, inLen);
+ BigInteger result = ProcessInput(input);
+ return core.ConvertOutput(result);
+ }
- BigInteger result;
- if (key is RsaPrivateCrtKeyParameters crt)
- {
- BigInteger e = crt.PublicExponent;
- BigInteger m = crt.Modulus;
- BigInteger r = BigIntegers.CreateRandomInRange(
- BigInteger.One, m.Subtract(BigInteger.One), random);
-
- BigInteger blindedInput = r.ModPow(e, m).Multiply(input).Mod(m);
- BigInteger blindedResult = core.ProcessBlock(blindedInput);
+ private BigInteger ProcessInput(BigInteger input)
+ {
+ if (!(key is RsaPrivateCrtKeyParameters crt))
+ return core.ProcessBlock(input);
- BigInteger rInv = BigIntegers.ModOddInverse(m, r);
- result = blindedResult.Multiply(rInv).Mod(m);
+ BigInteger e = crt.PublicExponent;
+ BigInteger m = crt.Modulus;
- // defence against Arjen Lenstra’s CRT attack
- if (!input.Equals(result.ModPow(e, m)))
- throw new InvalidOperationException("RSA engine faulty decryption/signing detected");
- }
- else
- {
- result = core.ProcessBlock(input);
- }
+ BigInteger r = BigIntegers.CreateRandomInRange(BigInteger.One, m.Subtract(BigInteger.One), random);
+ BigInteger blind = r.ModPow(e, m);
+ BigInteger unblind = BigIntegers.ModOddInverse(m, r);
- return core.ConvertOutput(result);
+ BigInteger blindedInput = blind.Multiply(input).Mod(m);
+ BigInteger blindedResult = core.ProcessBlock(blindedInput);
+ return unblind.Multiply(blindedResult).Mod(m);
}
}
}
diff --git a/crypto/src/crypto/engines/RSACoreEngine.cs b/crypto/src/crypto/engines/RSACoreEngine.cs
index ffa448b3d..ee0f86c3f 100644
--- a/crypto/src/crypto/engines/RSACoreEngine.cs
+++ b/crypto/src/crypto/engines/RSACoreEngine.cs
@@ -113,38 +113,42 @@ namespace Org.BouncyCastle.Crypto.Engines
: BigIntegers.AsUnsignedByteArray(result);
}
- public virtual BigInteger ProcessBlock(
- BigInteger input)
+ public virtual BigInteger ProcessBlock(BigInteger input)
{
CheckInitialised();
- if (key is RsaPrivateCrtKeyParameters crt)
- {
- //
- // we have the extra factors, use the Chinese Remainder Theorem - the author
- // wishes to express his thanks to Dirk Bonekaemper at rtsffm.com for
- // advice regarding the expression of this.
- //
- BigInteger p = crt.P;
- BigInteger q = crt.Q;
- BigInteger dP = crt.DP;
- BigInteger dQ = crt.DQ;
- BigInteger qInv = crt.QInv;
-
- // mP = ((input Mod p) ^ dP)) Mod p
- BigInteger mP = (input.Remainder(p)).ModPow(dP, p);
-
- // mQ = ((input Mod q) ^ dQ)) Mod q
- BigInteger mQ = (input.Remainder(q)).ModPow(dQ, q);
-
- // h = qInv * (mP - mQ) Mod p
- BigInteger h = mP.Subtract(mQ).Multiply(qInv).Mod(p);
-
- // m = h * q + mQ
- return h.Multiply(q).Add(mQ);
- }
+ if (!(key is RsaPrivateCrtKeyParameters crt))
+ return input.ModPow(key.Exponent, key.Modulus);
+
+ //
+ // we have the extra factors, use the Chinese Remainder Theorem - the author
+ // wishes to express his thanks to Dirk Bonekaemper at rtsffm.com for
+ // advice regarding the expression of this.
+ //
+ BigInteger p = crt.P;
+ BigInteger q = crt.Q;
+ BigInteger dP = crt.DP;
+ BigInteger dQ = crt.DQ;
+ BigInteger qInv = crt.QInv;
+
+ // mP = ((input Mod p) ^ dP)) Mod p
+ BigInteger mP = (input.Remainder(p)).ModPow(dP, p);
+
+ // mQ = ((input Mod q) ^ dQ)) Mod q
+ BigInteger mQ = (input.Remainder(q)).ModPow(dQ, q);
+
+ // h = qInv * (mP - mQ) Mod p
+ BigInteger h = mP.Subtract(mQ).Multiply(qInv).Mod(p);
+
+ // m = h * q + mQ
+ BigInteger m = h.Multiply(q).Add(mQ);
+
+ // defence against Arjen Lenstra’s CRT attack
+ BigInteger check = m.ModPow(crt.PublicExponent, crt.Modulus);
+ if (!check.Equals(input))
+ throw new InvalidOperationException("RSA engine faulty decryption/signing detected");
- return input.ModPow(key.Exponent, key.Modulus);
+ return m;
}
}
}
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