arcfour stream cipher for utility work

src/arcfour.h

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+
+/*
+ * This file is part of Codecrypt.
+ *
+ * Codecrypt is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Codecrypt is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with Codecrypt. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _ccr_rc4_h_
+#define _ccr_rc4_h_
+
+#include <vector>
+
+template<class inttype> class arcfour {
+	std::vector<inttype> S;
+	inttype I,J;
+	size_t mod;
+public:
+	bool init(size_t bits) {
+		if(bits>8*sizeof(inttype)) return false;
+		I=J=0;
+		S.resize(1<<bits);
+		mod=1<<bits;
+		for(size_t i=0;i<(1<<bits);++i) {
+			S[i]=i;
+		}
+		return true;
+	}
+
+	void clear() {
+		I=J=0;
+		mod=0;
+		S.clear();
+	}
+
+	void load_key(const std::vector<inttype>&K) {
+		inttype j=0,t;
+		for(size_t i=0;i<mod;++i) {
+			j=(j+S[i]+K[i%K.size()])%mod;
+			t=S[j];
+			S[j]=S[i];
+			S[i]=t;
+		}
+	}
+
+	inttype gen() {
+		I=(I+1)%mod;
+		J=(J+S[I])%mod;
+
+		register inttype t;
+		t=S[J];
+		S[J]=S[I];
+		S[I]=t;
+
+		return S[(S[I]+S[J])%mod];
+	}
+
+	void discard(size_t n) {
+		for(size_t i=0;i<n;++i) gen();
+	}
+
+	void gen(size_t n, std::vector<inttype>&out) {
+		out.resize(n);
+		for(size_t i=0;i<n;++i) out[i]=gen();
+	}
+};
+
+#endif
+