diff --git a/ecdsa.h b/ecdsa.h
new file mode 100644
index 0000000..7a309a0
--- /dev/null
+++ b/ecdsa.h
@@ -0,0 +1,55 @@
+#ifndef _SECP256K1_ECDSA_
+#define _SECP256K1_ECDSA_
+
+namespace secp256k1 {
+
+bool ParsePubkey(GroupElemJac &elem, const unsigned char *pub, int size) {
+    if (size == 33 && (pub[0] == 0x02 || pub[0] == 0x03)) {
+        FieldElem x;
+        x.SetBytes(pub+1);
+        elem.SetCompressed(x, pub[0] == 0x03);
+    } else if (size == 65 && (pub[0] == 0x04 || pub[0] == 0x06 || pub[0] == 0x07)) {
+        FieldElem x,y;
+        x.SetBytes(pub+1);
+        y.SetBytes(pub+33);
+        elem = GroupElem(x,y);
+        if ((pub[0] == 0x06 || pub[0] == 0x07) && y.IsOdd() != (pub[0] == 0x07))
+            return false;
+    } else {
+        return false;
+    }
+    return elem.IsValid();
+}
+
+class Signature {
+private:
+    Number r,s;
+
+public:
+    bool Verify(Context &ctx, const GroupElemJac &pubkey, const Number &message) {
+        const GroupConstants &c = GetGroupConst();
+
+        if (r.IsNeg() || s.IsNeg())
+            return false;
+        if (r.IsZero() || s.IsZero())
+            return false;
+        if (r.Compare(c.order) >= 0 || s.Compare(c.order) >= 0)
+            return false;
+
+        Context ct(ctx);
+        Number sn(ct); sn.SetModInverse(ct, s, c.order);
+        Number u1(ct); u1.SetModMul(ct, sn, message, c.order);
+        Number u2(ct); u2.SetModMul(ct, sn, r, c.order);
+        GroupElemJac pr; ECMult(ct, pr, pubkey, u2, u1);
+        if (pr.IsInfinity())
+            return false;
+        FieldElem xr; pr.GetX(xr);
+        unsigned char xrb[32]; xr.GetBytes(xrb);
+        Number xrn(ct); xrn.SetBytes(xrb,32); xrn.SetMod(ct,xrn,c.order);
+        return xrn.Compare(r) == 0;
+    }
+};
+
+}
+
+#endif
diff --git a/group.h b/group.h
index 880ac3e..b9b0837 100644
--- a/group.h
+++ b/group.h
@@ -39,6 +39,14 @@ public:
         y.SetNeg(y, 1);
     }
 
+    void GetX(FieldElem &xout) const {
+        xout = x;
+    }
+
+    void GetY(FieldElem &yout) const {
+        yout = y;
+    }
+
     std::string ToString() const {
         if (fInfinity)
             return "(inf)";
@@ -101,6 +109,24 @@ public:
         aff.y = y;
     }
 
+    void GetX(FieldElem &xout) {
+        FieldElem zi;
+        zi.SetInverse(z);
+        zi.SetSquare(zi);
+        xout.SetMult(x, zi);
+    }
+
+    bool IsInfinity() const {
+        return fInfinity;
+    }
+
+    void GetY(FieldElem &yout) {
+        FieldElem zi;
+        zi.SetInverse(z);
+        FieldElem zi3; zi3.SetSquare(zi); zi3.SetMult(zi, zi3);
+        yout.SetMult(y, zi3);
+    }
+
     void SetNeg(const GroupElemJac &p) {
         *this = p;
         y.Normalize();
diff --git a/num.h b/num.h
index bff7f16..78e5a62 100644
--- a/num.h
+++ b/num.h
@@ -71,8 +71,8 @@ public:
     void SetModInverse(Context &ctx, const Number &x, const Number &m) {
         BN_mod_inverse(bn, x.bn, m.bn, ctx);
     }
-    void SetModMul(Context &ctx, const Number &f, const Number &m) {
-        BN_mod_mul(bn, bn, f.bn, m.bn, ctx);
+    void SetModMul(Context &ctx, const Number &a, const Number &b, const Number &m) {
+        BN_mod_mul(bn, a.bn, b.bn, m.bn, ctx);
     }
     void SetAdd(Context &ctx, const Number &a1, const Number &a2) {
         BN_add(bn, a1.bn, a2.bn);
@@ -86,6 +86,12 @@ public:
     void SetDiv(Context &ctx, const Number &a1, const Number &a2) {
         BN_div(bn, NULL, a1.bn, a2.bn, ctx);
     }
+    void SetMod(Context &ctx, const Number &a, const Number &m) {
+        BN_nnmod(bn, m.bn, a.bn, ctx);
+    }
+    int Compare(const Number &a) {
+        return BN_cmp(bn, a.bn);
+    }
     int GetBits() const {
         return BN_num_bits(bn);
     }
@@ -99,7 +105,7 @@ public:
         BN_rshift(bn, bn, bits);
         return ret;
     }
-    // check whether number is 0
+    // check whether number is 0,
     bool IsZero() {
         return BN_is_zero(bn);
     }
diff --git a/secp256k1.cpp b/secp256k1.cpp
index 5965c2b..f7ad1dd 100644
--- a/secp256k1.cpp
+++ b/secp256k1.cpp
@@ -4,6 +4,7 @@
 #include "field.h"
 #include "group.h"
 #include "ecmult.h"
+#include "ecdsa.h"
 
 using namespace secp256k1;