diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6adb05e..e2bbb22 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,7 +24,7 @@ SET( DEFAULT_LIBRARY_INSTALL_DIR lib/ )
 SET( DEFAULT_EXECUTABLE_INSTALL_DIR bin/ )
 SET( CMAKE_DEBUG_POSTFIX _debug )
 SET( BUILD_SHARED_LIBS NO )
-SET( ECC_IMPL secp256k1 ) # openssl or secp256k1
+SET( ECC_IMPL openssl CACHE STRING "openssl or secp256k1" )
 
 set(platformBitness 32)
 if(CMAKE_SIZEOF_VOID_P EQUAL 8)
@@ -261,8 +261,8 @@ target_include_directories(fc
     ${CMAKE_CURRENT_SOURCE_DIR}/vendor/websocketpp
   )
 
-#target_link_libraries( fc PUBLIC easylzma_static scrypt udt ${Boost_LIBRARIES} ${OPENSSL_LIBRARIES} ${ZLIB_LIBRARIES} ${PLATFORM_SPECIFIC_LIBS} ${RPCRT4} ${CMAKE_DL_LIBS} ${rt_library})
-target_link_libraries( fc PUBLIC easylzma_static udt ${Boost_LIBRARIES} ${OPENSSL_LIBRARIES} ${ZLIB_LIBRARIES} ${PLATFORM_SPECIFIC_LIBS} ${RPCRT4} ${CMAKE_DL_LIBS} ${rt_library} ${readline_libraries} ${ECC_LIB})
+#target_link_libraries( fc PUBLIC easylzma_static scrypt udt ${Boost_LIBRARIES} ${OPENSSL_LIBRARIES} ${ZLIB_LIBRARIES} ${PLATFORM_SPECIFIC_LIBS} ${RPCRT4} ${CMAKE_DL_LIBS} ${rt_library} ${ECC_LIB} )
+target_link_libraries( fc PUBLIC easylzma_static udt ${Boost_LIBRARIES} ${OPENSSL_LIBRARIES} ${ZLIB_LIBRARIES} ${PLATFORM_SPECIFIC_LIBS} ${RPCRT4} ${CMAKE_DL_LIBS} ${rt_library} ${readline_libraries} ${ECC_LIB} )
 
 IF(NOT Boost_UNIT_TEST_FRAMEWORK_LIBRARY MATCHES "\\.(a|lib)$")
 IF(WIN32)
diff --git a/README-ecc.md b/README-ecc.md
new file mode 100644
index 0000000..8c1046a
--- /dev/null
+++ b/README-ecc.md
@@ -0,0 +1,55 @@
+ECC Support
+===========
+
+include/fc/crypto/elliptic.hpp defines an interface for some cryptographic
+wrapper classes handling elliptic curve cryptography.
+
+Two implementations of this interface exist. One is based on OpenSSL, the
+other is based on libsecp256k1 (see https://github.com/bitcoin/secp256k1 ).
+The implementation to be used is selected at compile time using the
+cmake variable "ECC_IMPL". It can take two values, openssl or secp256k1 .
+The default is "openssl". The alternative can be configured when invoking
+cmake, for example
+
+cmake -D ECC_IMPL=secp256k1 .
+
+If secp256k1 is chosen, the secp256k1 library and its include file must
+already be installed in the appropriate library / include directories on
+your system.
+
+
+Testing
+-------
+
+Type "make ecc_test" to build the ecc_test executable from tests/ecc_test.cpp
+with the currently configured ECC implementation.
+
+ecc_test expects two arguments:
+
+ecc_test <pass> <interop-file>
+
+<pass> is a somewhat arbitrary password used for testing.
+
+<interop-file> is a data file containing intermediate test results.
+If the file does not exist, it will be created and intermediate results from
+the current ECC backend are written to it.
+If the file does exist, intermediate results from the current ECC backend
+are compared with the file contents.
+
+For a full round of interoperability testing, you need to do this:
+
+1. Build ecc_test with openssl backend.
+2. Run "ecc_test test ecc.interop.openssl".
+3. Run "ecc_test test ecc.interop.openssl" again, testing openssl against
+   itself.
+4. Build ecc_test with secp256k1 backend.
+5. Run "ecc_test test ecc.interop.secp256k1".
+6. Run "ecc_test test ecc.interop.secp256k1" again, testing secp256k1 against
+   itself.
+7. Run "ecc_test test ecc.interop.openssl", testing secp256k1 against openssl.
+8. Build ecc_test with openssl backend.
+9. Run "ecc_test test ecc.interop.secp256k1", testing openssl against secp256k1.
+
+None of the test runs should produce any output. The above steps are scripted
+in tests//ecc-interop.sh .
+
diff --git a/tests/ecc-interop.sh b/tests/ecc-interop.sh
new file mode 100755
index 0000000..50ff0c7
--- /dev/null
+++ b/tests/ecc-interop.sh
@@ -0,0 +1,35 @@
+#!/bin/sh
+
+#TIME=time
+
+cd "`dirname $0`"/..
+
+echo Building ecc_test with openssl...
+(
+cmake -D ECC_IMPL=openssl .
+make ecc_test
+mv ecc_test ecc_test.openssl
+) >/dev/null 2>&1
+
+echo Building ecc_test with secp256k1...
+(
+cmake -D ECC_IMPL=secp256k1 .
+make ecc_test
+mv ecc_test ecc_test.secp256k1
+) >/dev/null 2>&1
+
+run () {
+    echo "Running ecc_test.$1 test ecc.interop.$1 ..."
+    $TIME "./ecc_test.$1" test "ecc.interop.$1"
+}
+
+run openssl
+run openssl
+run secp256k1
+run secp256k1
+run secp256k1
+run openssl
+
+echo Done.
+
+rm -f ecc_test.openssl ecc_test.secp256k1 ecc.interop.openssl ecc.interop.secp256k1