Fix ECP leakage in Add() and Double() (GH #869, PR #871)

This check-in provides the fix for leaks in ECP's Add() and Double(). The fixes were taken from Joost Renes, Craig Costello, and Lejla Batina's [Complete addition formulas for prime order elliptic curves](https://eprint.iacr.org/2015/1060.pdf).

The Pull Request includes two additional changes that were related to testing the primary fix. First, an `AuthenticatedKeyAgreementWithRolesValidate` interface was added. It allows us to test key agreement when roles are involved. Roles are "client", "server", "initiator", "recipient", etc.

Second, `SetGlobalSeed` was added to `test.cpp` to help with reproducible results. We had code in two different places that set the seed value for the random number generator. But it was sloppy and doing a poor job since results could not be reproduced under some circumstances.

1 files changed, 6 insertions, 5 deletions

diff --git a/ec2n.cpp b/ec2n.cpp
index 97763232..7b6cf451 100644
--- a/ec2n.cpp
+++ b/ec2n.cpp
@@ -16,7 +16,8 @@ ANONYMOUS_NAMESPACE_BEGIN
 using CryptoPP::EC2N;

 

 #if defined(HAVE_GCC_INIT_PRIORITY)

-  const EC2N::Point g_identity __attribute__ ((init_priority (CRYPTOPP_INIT_PRIORITY + 50))) = EC2N::Point();

+  #define INIT_ATTRIBUTE __attribute__ ((init_priority (CRYPTOPP_INIT_PRIORITY + 51)))

+  const EC2N::Point g_identity INIT_ATTRIBUTE = EC2N::Point();

 #elif defined(HAVE_MSC_INIT_PRIORITY)

   #pragma warning(disable: 4075)

   #pragma init_seg(".CRT$XCU")

@@ -51,8 +52,8 @@ void EC2N::DEREncode(BufferedTransformation &bt) const
 {

 	m_field->DEREncode(bt);

 	DERSequenceEncoder seq(bt);

-	m_field->DEREncodeElement(seq, m_a);

-	m_field->DEREncodeElement(seq, m_b);

+	   m_field->DEREncodeElement(seq, m_a);

+	   m_field->DEREncodeElement(seq, m_b);

 	seq.MessageEnd();

 }

 

@@ -260,7 +261,7 @@ const EC2N::Point& EC2N::Double(const Point &P) const
 

 // ********************************************************

 

-/*

+#if 0

 EcPrecomputation<EC2N>& EcPrecomputation<EC2N>::operator=(const EcPrecomputation<EC2N> &rhs)

 {

 	m_ec = rhs.m_ec;

@@ -312,7 +313,7 @@ EC2N::Point EcPrecomputation<EC2N>::CascadeExponentiate(const Integer &exponent,
 {

 	return m_ep.CascadeExponentiate(exponent, static_cast<const EcPrecomputation<EC2N> &>(pc2).m_ep, exponent2);

 }

-*/

+#endif

 

 NAMESPACE_END