Add KeyPairGenerator.EC backed by Android KeyStore.

The Android KeyStore backed KeyPairGenerator can generate EC key
pairs, but it cannot be instantiated via the standard JCA approach of
KeyPairGenerator.getInstance("EC", "AndroidKeyStore"). Instead, the
user must invoke KeyPairGenerator.getInstance("RSA",
"AndroidKeyStore") and then tell it to generate an EC key pair.

This CL fixes this weirdness.

The fix requires the introduction of late resolution of key algorithm
and default key size. Prior to this CL, these parameters were resolved
prior to KeyPairGenerator initialization, inside KeyPairGeneratorSpec.
In this CL, these parameters are resolved during KeyPairGenerator
initialization. This is fine because KeyPairGeneratorSpec should be as
dumb as possible and all the logic should reside in KeyPairGenerator
and lower layers.

Bug: 19018089
Change-Id: I114502356e6c9691518cf05b6d9eb0920b4fe0b2

1 files changed, 134 insertions, 20 deletions

diff --git a/keystore/java/android/security/AndroidKeyPairGenerator.java b/keystore/java/android/security/AndroidKeyPairGenerator.java
index a0ffb5f0d75c..9d9a173353c5 100644
--- a/keystore/java/android/security/AndroidKeyPairGenerator.java
+++ b/keystore/java/android/security/AndroidKeyPairGenerator.java
@@ -50,10 +50,50 @@ import java.security.spec.X509EncodedKeySpec;
  *
  * {@hide}
  */
-public class AndroidKeyPairGenerator extends KeyPairGeneratorSpi {
+public abstract class AndroidKeyPairGenerator extends KeyPairGeneratorSpi {
+
+    public static class RSA extends AndroidKeyPairGenerator {
+        public RSA() {
+            super("RSA");
+        }
+    }
+
+    public static class EC extends AndroidKeyPairGenerator {
+        public EC() {
+            super("EC");
+        }
+    }
+
+    /*
+     * These must be kept in sync with system/security/keystore/defaults.h
+     */
+
+    /* EC */
+    private static final int EC_DEFAULT_KEY_SIZE = 256;
+    private static final int EC_MIN_KEY_SIZE = 192;
+    private static final int EC_MAX_KEY_SIZE = 521;
+
+    /* RSA */
+    private static final int RSA_DEFAULT_KEY_SIZE = 2048;
+    private static final int RSA_MIN_KEY_SIZE = 512;
+    private static final int RSA_MAX_KEY_SIZE = 8192;
+
+    private final String mAlgorithm;
+
     private android.security.KeyStore mKeyStore;
 
     private KeyPairGeneratorSpec mSpec;
+    private String mKeyAlgorithm;
+    private int mKeyType;
+    private int mKeySize;
+
+    protected AndroidKeyPairGenerator(String algorithm) {
+        mAlgorithm = algorithm;
+    }
+
+    public String getAlgorithm() {
+        return mAlgorithm;
+    }
 
     /**
      * Generate a KeyPair which is backed by the Android keystore service. You
@@ -88,12 +128,11 @@ public class AndroidKeyPairGenerator extends KeyPairGeneratorSpi {
 
         Credentials.deleteAllTypesForAlias(mKeyStore, alias);
 
-        final int keyType = KeyStore.getKeyTypeForAlgorithm(mSpec.getKeyType());
-        byte[][] args = getArgsForKeyType(keyType, mSpec.getAlgorithmParameterSpec());
+        byte[][] args = getArgsForKeyType(mKeyType, mSpec.getAlgorithmParameterSpec());
 
         final String privateKeyAlias = Credentials.USER_PRIVATE_KEY + alias;
-        if (!mKeyStore.generate(privateKeyAlias, KeyStore.UID_SELF, keyType,
-                mSpec.getKeySize(), mSpec.getFlags(), args)) {
+        if (!mKeyStore.generate(privateKeyAlias, KeyStore.UID_SELF, mKeyType, mKeySize,
+                mSpec.getFlags(), args)) {
             throw new IllegalStateException("could not generate key in keystore");
         }
 
@@ -109,7 +148,7 @@ public class AndroidKeyPairGenerator extends KeyPairGeneratorSpi {
 
         final PublicKey pubKey;
         try {
-            final KeyFactory keyFact = KeyFactory.getInstance(mSpec.getKeyType());
+            final KeyFactory keyFact = KeyFactory.getInstance(mKeyAlgorithm);
             pubKey = keyFact.generatePublic(new X509EncodedKeySpec(pubKeyBytes));
         } catch (NoSuchAlgorithmException e) {
             throw new IllegalStateException("Can't instantiate key generator", e);
@@ -117,18 +156,9 @@ public class AndroidKeyPairGenerator extends KeyPairGeneratorSpi {
             throw new IllegalStateException("keystore returned invalid key encoding", e);
         }
 
-        final X509V3CertificateGenerator certGen = new X509V3CertificateGenerator();
-        certGen.setPublicKey(pubKey);
-        certGen.setSerialNumber(mSpec.getSerialNumber());
-        certGen.setSubjectDN(mSpec.getSubjectDN());
-        certGen.setIssuerDN(mSpec.getSubjectDN());
-        certGen.setNotBefore(mSpec.getStartDate());
-        certGen.setNotAfter(mSpec.getEndDate());
-        certGen.setSignatureAlgorithm(getDefaultSignatureAlgorithmForKeyType(mSpec.getKeyType()));
-
         final X509Certificate cert;
         try {
-            cert = certGen.generate(privKey);
+            cert = generateCertificate(privKey, pubKey);
         } catch (Exception e) {
             Credentials.deleteAllTypesForAlias(mKeyStore, alias);
             throw new IllegalStateException("Can't generate certificate", e);
@@ -151,13 +181,78 @@ public class AndroidKeyPairGenerator extends KeyPairGeneratorSpi {
         return new KeyPair(pubKey, privKey);
     }
 
-    private static String getDefaultSignatureAlgorithmForKeyType(String keyType) {
-        if ("RSA".equalsIgnoreCase(keyType)) {
+    @SuppressWarnings("deprecation")
+    private X509Certificate generateCertificate(PrivateKey privateKey, PublicKey publicKey)
+            throws Exception {
+        final X509V3CertificateGenerator certGen = new X509V3CertificateGenerator();
+        certGen.setPublicKey(publicKey);
+        certGen.setSerialNumber(mSpec.getSerialNumber());
+        certGen.setSubjectDN(mSpec.getSubjectDN());
+        certGen.setIssuerDN(mSpec.getSubjectDN());
+        certGen.setNotBefore(mSpec.getStartDate());
+        certGen.setNotAfter(mSpec.getEndDate());
+        certGen.setSignatureAlgorithm(getDefaultSignatureAlgorithmForKeyAlgorithm(mKeyAlgorithm));
+        return certGen.generate(privateKey);
+    }
+
+    private String getKeyAlgorithm(KeyPairGeneratorSpec spec) {
+        String result = spec.getKeyType();
+        if (result != null) {
+            return result;
+        }
+        return getAlgorithm();
+    }
+
+    private static int getDefaultKeySize(int keyType) {
+        if (keyType == NativeCrypto.EVP_PKEY_EC) {
+            return EC_DEFAULT_KEY_SIZE;
+        } else if (keyType == NativeCrypto.EVP_PKEY_RSA) {
+            return RSA_DEFAULT_KEY_SIZE;
+        }
+        return -1;
+    }
+
+    private static void checkValidKeySize(String keyAlgorithm, int keyType, int keySize)
+            throws InvalidAlgorithmParameterException {
+        if (keyType == NativeCrypto.EVP_PKEY_EC) {
+            if (keySize < EC_MIN_KEY_SIZE || keySize > EC_MAX_KEY_SIZE) {
+                throw new InvalidAlgorithmParameterException("EC keys must be >= "
+                        + EC_MIN_KEY_SIZE + " and <= " + EC_MAX_KEY_SIZE);
+            }
+        } else if (keyType == NativeCrypto.EVP_PKEY_RSA) {
+            if (keySize < RSA_MIN_KEY_SIZE || keySize > RSA_MAX_KEY_SIZE) {
+                throw new InvalidAlgorithmParameterException("RSA keys must be >= "
+                        + RSA_MIN_KEY_SIZE + " and <= " + RSA_MAX_KEY_SIZE);
+            }
+        } else {
+            throw new InvalidAlgorithmParameterException(
+                "Unsupported key algorithm: " + keyAlgorithm);
+        }
+    }
+
+    private static void checkCorrectParametersSpec(int keyType, int keySize,
+            AlgorithmParameterSpec spec) throws InvalidAlgorithmParameterException {
+        if (keyType == NativeCrypto.EVP_PKEY_RSA && spec != null) {
+            if (spec instanceof RSAKeyGenParameterSpec) {
+                RSAKeyGenParameterSpec rsaSpec = (RSAKeyGenParameterSpec) spec;
+                if (keySize != -1 && keySize != rsaSpec.getKeysize()) {
+                    throw new InvalidAlgorithmParameterException("RSA key size must match: "
+                            + keySize + " vs " + rsaSpec.getKeysize());
+                }
+            } else {
+                throw new InvalidAlgorithmParameterException(
+                    "RSA may only use RSAKeyGenParameterSpec");
+            }
+        }
+    }
+
+    private static String getDefaultSignatureAlgorithmForKeyAlgorithm(String algorithm) {
+        if ("RSA".equalsIgnoreCase(algorithm)) {
             return "sha256WithRSA";
-        } else if ("EC".equalsIgnoreCase(keyType)) {
+        } else if ("EC".equalsIgnoreCase(algorithm)) {
             return "sha256WithECDSA";
         } else {
-            throw new IllegalArgumentException("Unsupported key type " + keyType);
+            throw new IllegalArgumentException("Unsupported key type " + algorithm);
         }
     }
 
@@ -190,7 +285,26 @@ public class AndroidKeyPairGenerator extends KeyPairGeneratorSpi {
         }
 
         KeyPairGeneratorSpec spec = (KeyPairGeneratorSpec) params;
+        String keyAlgorithm = getKeyAlgorithm(spec);
+        int keyType = KeyStore.getKeyTypeForAlgorithm(keyAlgorithm);
+        if (keyType == -1) {
+            throw new InvalidAlgorithmParameterException(
+                    "Unsupported key algorithm: " + keyAlgorithm);
+        }
+        int keySize = spec.getKeySize();
+        if (keySize == -1) {
+            keySize = getDefaultKeySize(keyType);
+            if (keySize == -1) {
+                throw new InvalidAlgorithmParameterException(
+                    "Unsupported key algorithm: " + keyAlgorithm);
+            }
+        }
+        checkCorrectParametersSpec(keyType, keySize, spec.getAlgorithmParameterSpec());
+        checkValidKeySize(keyAlgorithm, keyType, keySize);
 
+        mKeyAlgorithm = keyAlgorithm;
+        mKeyType = keyType;
+        mKeySize = keySize;
         mSpec = spec;
         mKeyStore = android.security.KeyStore.getInstance();
     }