[crypto] allow selecting randomized ECDSA instead of deterministic (#7894)

There is no hard dependency in the Thread specification which requires
the use of deterministic signatures. On the contrary, looking at the
tinycrypt implementation, that one issues randomized ECDSA signatures
and seems to be quite happy with that.

This change does not change the default behaviour, which is to use
deterministic ECDSA when using the default MbedTLS backend. It does
however make it possible for platforms which have qualified hardware
entropy to select 'plain' ECDSA instead, which gives both a performance
and code size improvement on those platforms.

tests/unit/test_ecdsa.cpp

@@ -66,12 +66,14 @@ void TestEcdsaVector(void)
 
     const uint8_t kMessage[] = {'s', 'a', 'm', 'p', 'l', 'e'};
 
+#if OPENTHREAD_CONFIG_DETERMINISTIC_ECDSA_ENABLE
     const uint8_t kExpectedSignature[] = {
         0xEF, 0xD4, 0x8B, 0x2A, 0xAC, 0xB6, 0xA8, 0xFD, 0x11, 0x40, 0xDD, 0x9C, 0xD4, 0x5E, 0x81, 0xD6,
         0x9D, 0x2C, 0x87, 0x7B, 0x56, 0xAA, 0xF9, 0x91, 0xC3, 0x4D, 0x0E, 0xA8, 0x4E, 0xAF, 0x37, 0x16,
         0xF7, 0xCB, 0x1C, 0x94, 0x2D, 0x65, 0x7C, 0x41, 0xD4, 0x36, 0xC7, 0xA1, 0xB6, 0xE2, 0x9F, 0x65,
         0xF3, 0xE9, 0x00, 0xDB, 0xB9, 0xAF, 0xF4, 0x06, 0x4D, 0xC4, 0xAB, 0x2F, 0x84, 0x3A, 0xCD, 0xA8,
     };
+#endif
 
     Instance *instance = testInitInstance();
 
@@ -110,6 +112,7 @@ void TestEcdsaVector(void)
     SuccessOrQuit(keyPair.Sign(hash, signature));
     DumpBuffer("Signature", signature.GetBytes(), sizeof(signature));
 
+#if OPENTHREAD_CONFIG_DETERMINISTIC_ECDSA_ENABLE
     printf("\nCheck signature against expected sequence----------------------------------\n");
     DumpBuffer("Expected signature", kExpectedSignature, sizeof(kExpectedSignature));
 
@@ -117,6 +120,7 @@ void TestEcdsaVector(void)
     VerifyOrQuit(memcmp(signature.GetBytes(), kExpectedSignature, sizeof(kExpectedSignature)) == 0);
 
     printf("Signature matches expected sequence.\n");
+#endif
 
     printf("\nVerify the signature ------------------------------------------------------\n");
     SuccessOrQuit(publicKey.Verify(hash, signature));
@@ -125,7 +129,7 @@ void TestEcdsaVector(void)
     testFreeInstance(instance);
 }
 
-void TestEdsaKeyGenerationSignAndVerify(void)
+void TestEcdsaKeyGenerationSignAndVerify(void)
 {
     Instance *instance = testInitInstance();
 
@@ -183,7 +187,7 @@ int main(void)
 {
 #if OPENTHREAD_CONFIG_ECDSA_ENABLE
     ot::Crypto::TestEcdsaVector();
-    ot::Crypto::TestEdsaKeyGenerationSignAndVerify();
+    ot::Crypto::TestEcdsaKeyGenerationSignAndVerify();
     printf("All tests passed\n");
 #else
     printf("ECDSA feature is not enabled\n");