a

libsec/egdecrypt.c

@@ -0,0 +1,28 @@
+#include "os.h"
+#include <mp.h>
+#include <libsec.h>
+
+mpint*
+egdecrypt(EGpriv *priv, mpint *in, mpint *out)
+{
+	EGpub *pub = &priv->pub;
+	mpint *gamma, *delta;
+	mpint *p = pub->p;
+	int plen = mpsignif(p)+1;
+	int shift = ((plen+Dbits-1)/Dbits)*Dbits;
+
+	if(out == nil)
+		out = mpnew(0);
+	gamma = mpnew(0);
+	delta = mpnew(0);
+	mpright(in, shift, gamma);
+	mpleft(gamma, shift, delta);
+	mpsub(in, delta, delta);	
+	mpexp(gamma, priv->secret, p, out);
+	mpinvert(out, p, gamma);
+	mpmul(gamma, delta, out);
+	mpmod(out, p, out);
+	mpfree(gamma);
+	mpfree(delta);
+	return out;
+}