Add German digital signature algorithm (ECGDSA) (Issue 113)

Also see ISO/IEC 15946 and http://www.teletrust.de/fileadmin/files/oid/ecgdsa_final.pdf

1 files changed, 37 insertions, 0 deletions

diff --git a/gfpcrypt.h b/gfpcrypt.h
index 00514d35..0d3c8393 100644
--- a/gfpcrypt.h
+++ b/gfpcrypt.h
@@ -393,6 +393,43 @@ private:
 	mutable HMAC<H> m_hmac;

 };

 

+//! \class DL_Algorithm_GDSA_ISO15946

+//! \brief German Digital Signature Algorithm

+//! \tparam T FieldElement type or class

+//! \sa Erwin Hess, Marcus Schafheutle, and Pascale Serf <A HREF="http://www.teletrust.de/fileadmin/files/oid/ecgdsa_final.pdf">The

+//!   Digital Signature Scheme ECGDSA (October 24, 2006)</A>

+template <class T>

+class DL_Algorithm_GDSA_ISO15946 : public DL_ElgamalLikeSignatureAlgorithm<T>

+{

+public:

+	CRYPTOPP_STATIC_CONSTEXPR const char* CRYPTOPP_API StaticAlgorithmName() {return "GDSA-ISO15946";}

+

+	virtual ~DL_Algorithm_GDSA_ISO15946() {}

+

+	void Sign(const DL_GroupParameters<T> &params, const Integer &x, const Integer &k, const Integer &e, Integer &r, Integer &s) const

+	{

+		const Integer &q = params.GetSubgroupOrder();

+		// r = x(k * G) mod q

+		r = params.ConvertElementToInteger(params.ExponentiateBase(k)) % q;

+		// s = (k * r − h(m)) * d_A mod q

+		s = a_times_b_mod_c(k * r - e, x, q);

+		CRYPTOPP_ASSERT(!!r && !!s);

+	}

+

+	bool Verify(const DL_GroupParameters<T> &params, const DL_PublicKey<T> &publicKey, const Integer &e, const Integer &r, const Integer &s) const

+	{

+		const Integer &q = params.GetSubgroupOrder();

+		if (r>=q || r<1 || s>=q || s<1)

+			return false;

+

+		const Integer& rInv = r.InverseMod(q);

+		Integer u1 = (rInv * e) % q;

+		Integer u2 = (rInv * s) % q;

+		// verify x(G^u1 + P_A^u2) mod q

+		return r == params.ConvertElementToInteger(publicKey.CascadeExponentiateBaseAndPublicElement(u1, u2)) % q;

+	}

+};

+

 CRYPTOPP_DLL_TEMPLATE_CLASS DL_Algorithm_GDSA<Integer>;

 CRYPTOPP_DLL_TEMPLATE_CLASS DL_Algorithm_DSA_RFC6979<Integer, SHA1>;

 CRYPTOPP_DLL_TEMPLATE_CLASS DL_Algorithm_DSA_RFC6979<Integer, SHA224>;