crypto: support explicit EC curve generation

include/opendht/crypto.h

@@ -204,7 +204,13 @@ struct OPENDHT_PUBLIC PrivateKey
      * @param algo : the public key algorithm to use, GNUTLS_PK_RSA or GNUTLS_PK_RSA_OAEP
      */
     static PrivateKey generate(unsigned key_length = 4096, gnutls_pk_algorithm_t algo = GNUTLS_PK_RSA);
-    static PrivateKey generateEC();
+
+    /**
+     * Generate a new EC key pair
+     * @param curve : the elliptic curve to use. If GNUTLS_ECC_CURVE_INVALID is provided, the default curve will be used
+     * (currently GNUTLS_ECC_CURVE_SECP384R1).
+     */
+    static PrivateKey generateEC(gnutls_ecc_curve_t curve = GNUTLS_ECC_CURVE_INVALID);
 
     gnutls_privkey_t key {};
     gnutls_x509_privkey_t x509_key {};
@@ -272,7 +278,8 @@ public:
      * and incremented on subsequent ones.
      */
     void sign(const PrivateKey&, const Certificate&, duration validity_period = {}, uint64_t number = 0);
-    void sign(const Identity& id, duration validity_period = {}, uint64_t number = 0) {
+    void sign(const Identity& id, duration validity_period = {}, uint64_t number = 0)
+    {
         sign(*id.first, *id.second, validity_period, number);
     }
 

src/crypto.cpp

@@ -1294,14 +1294,16 @@ PrivateKey::generate(unsigned key_length, gnutls_pk_algorithm_t algo)
 }
 
 PrivateKey
-PrivateKey::generateEC()
+PrivateKey::generateEC(gnutls_ecc_curve_t curve)
 {
     gnutls_x509_privkey_t key;
     if (gnutls_x509_privkey_init(&key) != GNUTLS_E_SUCCESS)
         throw CryptoException("Unable to initialize private key.");
     int err = gnutls_x509_privkey_generate(key,
                                            GNUTLS_PK_EC,
-                                           gnutls_sec_param_to_pk_bits(GNUTLS_PK_EC, GNUTLS_SEC_PARAM_ULTRA),
+                                           curve == GNUTLS_ECC_CURVE_INVALID
+                                               ? gnutls_sec_param_to_pk_bits(GNUTLS_PK_EC, GNUTLS_SEC_PARAM_ULTRA)
+                                               : GNUTLS_CURVE_TO_BITS(curve),
                                            0);
     if (err != GNUTLS_E_SUCCESS) {
         gnutls_x509_privkey_deinit(key);

tests/test_crypto.cpp

@@ -327,6 +327,16 @@ CryptoTester::testCertificateSerialNumber()
     }
 }
 
+void
+CryptoTester::testEcKeyCurve()
+{
+    auto key = dht::crypto::PrivateKey::generateEC(GNUTLS_ECC_CURVE_SECP256R1);
+    unsigned int bits = 0;
+    CPPUNIT_ASSERT_EQUAL(static_cast<int>(GNUTLS_PK_EC),
+                         gnutls_x509_privkey_get_pk_algorithm2(key.x509_key, &bits));
+    CPPUNIT_ASSERT_EQUAL(256u, bits);
+}
+
 void
 CryptoTester::testOcsp()
 {

tests/test_crypto.h

@@ -19,6 +19,7 @@ class CryptoTester : public CppUnit::TestFixture
     CPPUNIT_TEST(testRevocationListPartitionedNumber);
     CPPUNIT_TEST(testCertificateRequest);
     CPPUNIT_TEST(testCertificateSerialNumber);
+    CPPUNIT_TEST(testEcKeyCurve);
     CPPUNIT_TEST(testOcsp);
     CPPUNIT_TEST(testAesEncryption);
     CPPUNIT_TEST(testAesEncryptionWithMultipleKeySizes);
@@ -68,6 +69,10 @@ public:
      * Test certificate serial number extraction
      */
     void testCertificateSerialNumber();
+    /**
+     * Test EC private key generation with an explicit curve
+     */
+    void testEcKeyCurve();
     /**
      * Test OCSP
      */