1 files changed, 49 insertions, 0 deletions
diff --git a/c5/blumshub.cpp b/c5/blumshub.cpp
new file mode 100644
index 0000000..f715c84
--- /dev/null
+++ b/c5/blumshub.cpp
@@ -0,0 +1,49 @@
+// blumshub.cpp - written and placed in the public domain by Wei Dai
+
+#include "pch.h"
+#include "blumshub.h"
+
+NAMESPACE_BEGIN(CryptoPP)
+
+PublicBlumBlumShub::PublicBlumBlumShub(const Integer &n, const Integer &seed)
+	: modn(n),
+	  maxBits(BitPrecision(n.BitCount())-1)
+{
+	current = modn.Square(modn.Square(seed));
+	bitsLeft = maxBits;
+}
+
+unsigned int PublicBlumBlumShub::GenerateBit()
+{
+	if (bitsLeft==0)
+	{
+		current = modn.Square(current);
+		bitsLeft = maxBits;
+	}
+
+	return current.GetBit(--bitsLeft);
+}
+
+byte PublicBlumBlumShub::GenerateByte()
+{
+	byte b=0;
+	for (int i=0; i<8; i++)
+		b = (b << 1) | PublicBlumBlumShub::GenerateBit();
+	return b;
+}
+
+BlumBlumShub::BlumBlumShub(const Integer &p, const Integer &q, const Integer &seed)
+	: PublicBlumBlumShub(p*q, seed),
+	  p(p), q(q),
+	  x0(modn.Square(seed))
+{
+}
+
+void BlumBlumShub::Seek(dword index)
+{
+	Integer e = a_exp_b_mod_c (2, ((index*8) / maxBits + 1), (p-1)*(q-1));
+	current = modn.Exponentiate(x0, e);
+	bitsLeft = maxBits - int((index*8) % maxBits);
+}
+
+NAMESPACE_END