Initial revision

git-svn-id: svn://svn.code.sf.net/p/cryptopp/code/trunk/c5@2 57ff6487-cd31-0410-9ec3-f628ee90f5f0

1 files changed, 116 insertions, 0 deletions

diff --git a/arc4.cpp b/arc4.cpp
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+++ b/arc4.cpp
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+// arc4.cpp - written and placed in the public domain by Wei Dai
+
+// The ARC4 algorithm was first revealed in an anonymous email to the
+// cypherpunks mailing list. This file originally contained some
+// code copied from this email. The code has since been rewritten in order
+// to clarify the copyright status of this file. It should now be
+// completely in the public domain.
+
+#include "pch.h"
+#include "arc4.h"
+
+NAMESPACE_BEGIN(CryptoPP)
+
+void ARC4_TestInstantiations()
+{
+	ARC4 x;
+}
+
+ARC4_Base::~ARC4_Base()
+{
+	m_x = m_y = 0;
+}
+
+void ARC4_Base::UncheckedSetKey(const NameValuePairs &params, const byte *key, unsigned int keyLen)
+{
+	AssertValidKeyLength(keyLen);
+
+	m_x = 1;
+	m_y = 0;
+
+	unsigned int i;
+	for (i=0; i<256; i++)
+		m_state[i] = i;
+
+	unsigned int keyIndex = 0, stateIndex = 0;
+	for (i=0; i<256; i++)
+	{
+		unsigned int a = m_state[i];
+		stateIndex += key[keyIndex] + a;
+		stateIndex &= 0xff;
+		m_state[i] = m_state[stateIndex];
+		m_state[stateIndex] = a;
+		if (++keyIndex >= keyLen)
+			keyIndex = 0;
+	}
+
+	int discardBytes = params.GetIntValueWithDefault("DiscardBytes", GetDefaultDiscardBytes());
+	DiscardBytes(discardBytes);
+}
+
+template <class T>
+static inline unsigned int MakeByte(T &x, T &y, byte *s)
+{
+	unsigned int a = s[x];
+	y = (y+a) & 0xff;
+	unsigned int b = s[y];
+	s[x] = b;
+	s[y] = a;
+	x = (x+1) & 0xff;
+	return s[(a+b) & 0xff];
+}
+
+byte ARC4_Base::GenerateByte()
+{
+	return MakeByte(m_x, m_y, m_state);
+}
+
+void ARC4_Base::ProcessData(byte *outString, const byte *inString, unsigned int length)
+{
+	if (length == 0)
+		return;
+
+	byte *const s = m_state;
+	unsigned int x = m_x;
+	unsigned int y = m_y;
+
+	if (inString == outString)
+	{
+		do
+		{
+			*outString++ ^= MakeByte(x, y, s);
+		} while (--length);
+	}
+	else
+	{
+		do
+		{
+			*outString++ = *inString++ ^ MakeByte(x, y, s);
+		}
+		while(--length);
+	}
+
+	m_x = x;
+	m_y = y;
+}
+
+void ARC4_Base::DiscardBytes(unsigned int length)
+{
+	if (length == 0)
+		return;
+
+	byte *const s = m_state;
+	unsigned int x = m_x;
+	unsigned int y = m_y;
+
+	do
+	{
+		MakeByte(x, y, s);
+	}
+	while(--length);
+
+	m_x = x;
+	m_y = y;
+}
+
+NAMESPACE_END