perf: avoid expensive call to Mac.getInstance

src/main/java/com/amazonaws/encryptionsdk/CryptoAlgorithm.java

@@ -7,6 +7,7 @@
 import com.amazonaws.encryptionsdk.internal.CommittedKey;
 import com.amazonaws.encryptionsdk.internal.Constants;
 import com.amazonaws.encryptionsdk.internal.HmacKeyDerivationFunction;
+import com.amazonaws.encryptionsdk.internal.MacAlgorithm;
 import com.amazonaws.encryptionsdk.model.CiphertextHeaders;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
@@ -342,7 +343,7 @@ private SecretKey getCommittedEncryptionKey(
 
   private SecretKey getNonCommittedEncryptionKey(
       final SecretKey dataKey, final CiphertextHeaders headers) throws InvalidKeyException {
-    final String macAlgorithm;
+    final MacAlgorithm macAlgorithm;
 
     switch (this) {
       case ALG_AES_128_GCM_IV12_TAG16_NO_KDF:
@@ -353,11 +354,11 @@ private SecretKey getNonCommittedEncryptionKey(
       case ALG_AES_192_GCM_IV12_TAG16_HKDF_SHA256:
       case ALG_AES_256_GCM_IV12_TAG16_HKDF_SHA256:
       case ALG_AES_128_GCM_IV12_TAG16_HKDF_SHA256_ECDSA_P256:
-        macAlgorithm = "HmacSHA256";
+        macAlgorithm = MacAlgorithm.HmacSHA256;
         break;
       case ALG_AES_192_GCM_IV12_TAG16_HKDF_SHA384_ECDSA_P384:
       case ALG_AES_256_GCM_IV12_TAG16_HKDF_SHA384_ECDSA_P384:
-        macAlgorithm = "HmacSHA384";
+        macAlgorithm = MacAlgorithm.HmacSHA384;
         break;
       default:
         throw new UnsupportedOperationException("Support for " + this + " not yet built.");
@@ -393,3 +394,4 @@ private SecretKey getNonCommittedEncryptionKey(
     return new SecretKeySpec(hkdf.deriveKey(info.array(), getKeyLength()), getKeyAlgo());
   }
 }
+

src/main/java/com/amazonaws/encryptionsdk/internal/CommittedKey.java

@@ -80,10 +80,10 @@ public static CommittedKey generate(CryptoAlgorithm alg, SecretKey dataKey, byte
               + rawDataKey.length);
     }
 
-    final String macAlgorithm;
+    final MacAlgorithm macAlgorithm;
     switch (alg.getKeyCommitmentAlgo_()) {
       case HKDF_SHA_512:
-        macAlgorithm = HMAC_SHA_512;
+        macAlgorithm = MacAlgorithm.HkdfSHA512;
         break;
       default:
         throw new UnsupportedOperationException(

src/main/java/com/amazonaws/encryptionsdk/internal/HmacKeyDerivationFunction.java

@@ -48,11 +48,9 @@ public final class HmacKeyDerivationFunction {
    * @throws NoSuchAlgorithmException if no Provider supports a MacSpi implementation for the
    *     specified algorithm.
    */
-  public static HmacKeyDerivationFunction getInstance(final String algorithm)
+  public static HmacKeyDerivationFunction getInstance(final MacAlgorithm algorithm)
       throws NoSuchAlgorithmException {
-    // Constructed specifically to sanity-test arguments.
-    Mac mac = Mac.getInstance(algorithm);
-    return new HmacKeyDerivationFunction(algorithm, mac.getProvider());
+    return new HmacKeyDerivationFunction(algorithm);
   }
 
   /**
@@ -94,12 +92,9 @@ public void init(final byte[] ikm, final byte[] salt) {
     }
   }
 
-  private HmacKeyDerivationFunction(final String algorithm, final Provider provider) {
-    isTrue(
-        algorithm.startsWith("Hmac"),
-        "Invalid algorithm " + algorithm + ". Hkdf may only be used with Hmac algorithms.");
-    this.algorithm = algorithm;
-    this.provider = provider;
+  private HmacKeyDerivationFunction(final MacAlgorithm algorithm) throws NoSuchAlgorithmException {
+    this.algorithm = algorithm.getAlgorithm();
+    this.provider = algorithm.getProvider();
   }
 
   /**

src/main/java/com/amazonaws/encryptionsdk/internal/MacAlgorithm.java

@@ -0,0 +1,32 @@
+package com.amazonaws.encryptionsdk.internal;
+
+import javax.crypto.Mac;
+import java.security.NoSuchAlgorithmException;
+import java.security.Provider;
+
+public enum MacAlgorithm {
+    HmacSHA256("HmacSHA256"),
+    HmacSHA384("HmacSHA384"),
+    HmacSHA512("HmacSHA512"),
+    HkdfSHA512("HkdfSHA512"),
+    HmacSHA1("HmacSHA1");
+    private final String algorithm;
+    private Provider provider;
+
+    MacAlgorithm(String algorithm) {
+        this.algorithm = algorithm;
+    }
+
+    Provider getProvider() throws NoSuchAlgorithmException {
+        Provider provider = this.provider;
+        if (provider == null) {
+            provider = Mac.getInstance(algorithm).getProvider();
+            this.provider = provider;
+        }
+        return provider;
+    }
+
+    String getAlgorithm() {
+        return algorithm;
+    }
+}

src/test/java/com/amazonaws/encryptionsdk/internal/CommittedKeyTest.java

@@ -108,7 +108,7 @@ public void testGenerateCommittedKeySmokeTest() throws Exception {
     final byte[] n1 = insecureRandomBytes(32);
 
     // Hash for HKDF is SHA-512
-    final HmacKeyDerivationFunction hkdf = HmacKeyDerivationFunction.getInstance("HmacSHA512");
+    final HmacKeyDerivationFunction hkdf = HmacKeyDerivationFunction.getInstance(MacAlgorithm.HmacSHA512);
 
     // K_R (Raw keying material, a.k.a. data key) is 256 bits (32 bytes)
     // Normally this needs to be cryptographically secure, but we can relax this for improved

src/test/java/com/amazonaws/encryptionsdk/internal/HmacKeyDerivationFunctionTest.java

@@ -21,7 +21,7 @@ public class HmacKeyDerivationFunctionTest {
   private static final testCase[] testCases =
       new testCase[] {
         new testCase(
-            "HmacSHA256",
+            MacAlgorithm.HmacSHA256,
             fromCHex(
                 "\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b"
                     + "\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b"),
@@ -30,7 +30,7 @@ public class HmacKeyDerivationFunctionTest {
             fromHex(
                 "3CB25F25FAACD57A90434F64D0362F2A2D2D0A90CF1A5A4C5DB02D56ECC4C5BF34007208D5B887185865")),
         new testCase(
-            "HmacSHA256",
+                MacAlgorithm.HmacSHA256,
             fromCHex(
                 "\\x00\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d"
                     + "\\x0e\\x0f\\x10\\x11\\x12\\x13\\x14\\x15\\x16\\x17\\x18\\x19\\x1a\\x1b"
@@ -60,7 +60,7 @@ public class HmacKeyDerivationFunctionTest {
                     + "CC30C58179EC3E87C14C01D5C1F3434F"
                     + "1D87")),
         new testCase(
-            "HmacSHA256",
+            MacAlgorithm.HmacSHA256,
             fromCHex(
                 "\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b"
                     + "\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b"),
@@ -71,7 +71,7 @@ public class HmacKeyDerivationFunctionTest {
                     + "B8A11F5C5EE1879EC3454E5F3C738D2D"
                     + "9D201395FAA4B61A96C8")),
         new testCase(
-            "HmacSHA1",
+            MacAlgorithm.HmacSHA1,
             fromCHex("\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b"),
             fromCHex("\\x00\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c"),
             fromCHex("\\xf0\\xf1\\xf2\\xf3\\xf4\\xf5\\xf6\\xf7\\xf8\\xf9"),
@@ -80,7 +80,7 @@ public class HmacKeyDerivationFunctionTest {
                     + "A4F14B822F5B091568A9CDD4F155FDA2"
                     + "C22E422478D305F3F896")),
         new testCase(
-            "HmacSHA1",
+            MacAlgorithm.HmacSHA1,
             fromCHex(
                 "\\x00\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d"
                     + "\\x0e\\x0f\\x10\\x11\\x12\\x13\\x14\\x15\\x16\\x17\\x18\\x19\\x1a\\x1b"
@@ -109,15 +109,15 @@ public class HmacKeyDerivationFunctionTest {
                     + "486EA37CE3D397ED034C7F9DFEB15C5E"
                     + "927336D0441F4C4300E2CFF0D0900B52D3B4")),
         new testCase(
-            "HmacSHA1",
+            MacAlgorithm.HmacSHA1,
             fromCHex(
                 "\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b"
                     + "\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b\\x0b"),
             new byte[0],
             new byte[0],
             fromHex("0AC1AF7002B3D761D1E55298DA9D0506" + "B9AE52057220A306E07B6B87E8DF21D0")),
         new testCase(
-            "HmacSHA1",
+            MacAlgorithm.HmacSHA1,
             fromCHex(
                 "\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c"
                     + "\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c\\x0c"),
@@ -200,13 +200,13 @@ private static byte[] fromCHex(String data) {
   }
 
   private static class testCase {
-    public final String algo;
+    public final MacAlgorithm algo;
     public final byte[] ikm;
     public final byte[] salt;
     public final byte[] info;
     public final byte[] expected;
 
-    testCase(String algo, byte[] ikm, byte[] salt, byte[] info, byte[] expected) {
+    testCase(MacAlgorithm algo, byte[] ikm, byte[] salt, byte[] info, byte[] expected) {
       super();
       this.algo = algo;
       this.ikm = ikm;