Pull SecureBox.java out into its own library.

SecureBox is needed by Settings for encrypting device credential and
was inaccessible from services/core/java/com/android/server.
Create a new SecureBox library to resolve.

Test: atest com.android.server.locksettings.recoverablekeystore
SecureBoxTests
Bug: 258505917

Change-Id: I65484edf12b04dfe1642cd0c97bc999d26430395

1 files changed, 461 insertions, 0 deletions

diff --git a/libs/securebox/src/com/android/security/SecureBox.java b/libs/securebox/src/com/android/security/SecureBox.java
new file mode 100644
index 000000000000..0ebaff4ac8e5
--- /dev/null
+++ b/libs/securebox/src/com/android/security/SecureBox.java
@@ -0,0 +1,461 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.security;
+
+import android.annotation.Nullable;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.util.ArrayUtils;
+
+import java.math.BigInteger;
+import java.nio.BufferUnderflowException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.KeyFactory;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.NoSuchAlgorithmException;
+import java.security.PrivateKey;
+import java.security.PublicKey;
+import java.security.SecureRandom;
+import java.security.interfaces.ECPublicKey;
+import java.security.spec.ECFieldFp;
+import java.security.spec.ECGenParameterSpec;
+import java.security.spec.ECParameterSpec;
+import java.security.spec.ECPoint;
+import java.security.spec.ECPublicKeySpec;
+import java.security.spec.EllipticCurve;
+import java.security.spec.InvalidKeySpecException;
+import java.util.Arrays;
+
+import javax.crypto.AEADBadTagException;
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.KeyAgreement;
+import javax.crypto.Mac;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.SecretKey;
+import javax.crypto.spec.GCMParameterSpec;
+import javax.crypto.spec.SecretKeySpec;
+
+/**
+ * Implementation of the SecureBox v2 crypto functions.
+ *
+ * <p>Securebox v2 provides a simple interface to perform encryptions by using any of the following
+ * credential types:
+ *
+ * <ul>
+ *   <li>A public key owned by the recipient,
+ *   <li>A secret shared between the sender and the recipient, or
+ *   <li>Both a recipient's public key and a shared secret.
+ * </ul>
+ *
+ * @hide
+ */
+public class SecureBox {
+
+    private static final byte[] VERSION = new byte[] {(byte) 0x02, 0}; // LITTLE_ENDIAN_TWO_BYTES(2)
+    private static final byte[] HKDF_SALT =
+            ArrayUtils.concat("SECUREBOX".getBytes(StandardCharsets.UTF_8), VERSION);
+    private static final byte[] HKDF_INFO_WITH_PUBLIC_KEY =
+            "P256 HKDF-SHA-256 AES-128-GCM".getBytes(StandardCharsets.UTF_8);
+    private static final byte[] HKDF_INFO_WITHOUT_PUBLIC_KEY =
+            "SHARED HKDF-SHA-256 AES-128-GCM".getBytes(StandardCharsets.UTF_8);
+    private static final byte[] CONSTANT_01 = {(byte) 0x01};
+    private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
+    private static final byte EC_PUBLIC_KEY_PREFIX = (byte) 0x04;
+
+    private static final String CIPHER_ALG = "AES";
+    private static final String EC_ALG = "EC";
+    private static final String EC_P256_COMMON_NAME = "secp256r1";
+    private static final String EC_P256_OPENSSL_NAME = "prime256v1";
+    private static final String ENC_ALG = "AES/GCM/NoPadding";
+    private static final String KA_ALG = "ECDH";
+    private static final String MAC_ALG = "HmacSHA256";
+
+    private static final int EC_COORDINATE_LEN_BYTES = 32;
+    private static final int EC_PUBLIC_KEY_LEN_BYTES = 2 * EC_COORDINATE_LEN_BYTES + 1;
+    private static final int GCM_NONCE_LEN_BYTES = 12;
+    private static final int GCM_KEY_LEN_BYTES = 16;
+    private static final int GCM_TAG_LEN_BYTES = 16;
+
+    private static final BigInteger BIG_INT_02 = BigInteger.valueOf(2);
+
+    private enum AesGcmOperation {
+        ENCRYPT,
+        DECRYPT
+    }
+
+    // Parameters for the NIST P-256 curve y^2 = x^3 + ax + b (mod p)
+    private static final BigInteger EC_PARAM_P =
+            new BigInteger("ffffffff00000001000000000000000000000000ffffffffffffffffffffffff", 16);
+    private static final BigInteger EC_PARAM_A = EC_PARAM_P.subtract(new BigInteger("3"));
+    private static final BigInteger EC_PARAM_B =
+            new BigInteger("5ac635d8aa3a93e7b3ebbd55769886bc651d06b0cc53b0f63bce3c3e27d2604b", 16);
+
+    @VisibleForTesting static final ECParameterSpec EC_PARAM_SPEC;
+
+    static {
+        EllipticCurve curveSpec =
+                new EllipticCurve(new ECFieldFp(EC_PARAM_P), EC_PARAM_A, EC_PARAM_B);
+        ECPoint generator =
+                new ECPoint(
+                        new BigInteger(
+                                "6b17d1f2e12c4247f8bce6e563a440f277037d812deb33a0f4a13945d898c296",
+                                16),
+                        new BigInteger(
+                                "4fe342e2fe1a7f9b8ee7eb4a7c0f9e162bce33576b315ececbb6406837bf51f5",
+                                16));
+        BigInteger generatorOrder =
+                new BigInteger(
+                        "ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551", 16);
+        EC_PARAM_SPEC = new ECParameterSpec(curveSpec, generator, generatorOrder, /* cofactor */ 1);
+    }
+
+    private SecureBox() {}
+
+    /**
+     * Randomly generates a public-key pair that can be used for the functions {@link #encrypt} and
+     * {@link #decrypt}.
+     *
+     * @return the randomly generated public-key pair
+     * @throws NoSuchAlgorithmException if the underlying crypto algorithm is not supported
+     * @hide
+     */
+    public static KeyPair genKeyPair() throws NoSuchAlgorithmException {
+        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(EC_ALG);
+        try {
+            // Try using the OpenSSL provider first
+            keyPairGenerator.initialize(new ECGenParameterSpec(EC_P256_OPENSSL_NAME));
+            return keyPairGenerator.generateKeyPair();
+        } catch (InvalidAlgorithmParameterException ex) {
+            // Try another name for NIST P-256
+        }
+        try {
+            keyPairGenerator.initialize(new ECGenParameterSpec(EC_P256_COMMON_NAME));
+            return keyPairGenerator.generateKeyPair();
+        } catch (InvalidAlgorithmParameterException ex) {
+            throw new NoSuchAlgorithmException("Unable to find the NIST P-256 curve", ex);
+        }
+    }
+
+    /**
+     * Encrypts {@code payload} by using {@code theirPublicKey} and/or {@code sharedSecret}. At
+     * least one of {@code theirPublicKey} and {@code sharedSecret} must be non-null, and an empty
+     * {@code sharedSecret} is equivalent to null.
+     *
+     * <p>Note that {@code header} will be authenticated (but not encrypted) together with {@code
+     * payload}, and the same {@code header} has to be provided for {@link #decrypt}.
+     *
+     * @param theirPublicKey the recipient's public key, or null if the payload is to be encrypted
+     *     only with the shared secret
+     * @param sharedSecret the secret shared between the sender and the recipient, or null if the
+     *     payload is to be encrypted only with the recipient's public key
+     * @param header the data that will be authenticated with {@code payload} but not encrypted, or
+     *     null if the data is empty
+     * @param payload the data to be encrypted, or null if the data is empty
+     * @return the encrypted payload
+     * @throws NoSuchAlgorithmException if any underlying crypto algorithm is not supported
+     * @throws InvalidKeyException if the provided key is invalid for underlying crypto algorithms
+     * @hide
+     */
+    public static byte[] encrypt(
+            @Nullable PublicKey theirPublicKey,
+            @Nullable byte[] sharedSecret,
+            @Nullable byte[] header,
+            @Nullable byte[] payload)
+            throws NoSuchAlgorithmException, InvalidKeyException {
+        sharedSecret = emptyByteArrayIfNull(sharedSecret);
+        if (theirPublicKey == null && sharedSecret.length == 0) {
+            throw new IllegalArgumentException("Both the public key and shared secret are empty");
+        }
+        header = emptyByteArrayIfNull(header);
+        payload = emptyByteArrayIfNull(payload);
+
+        KeyPair senderKeyPair;
+        byte[] dhSecret;
+        byte[] hkdfInfo;
+        if (theirPublicKey == null) {
+            senderKeyPair = null;
+            dhSecret = EMPTY_BYTE_ARRAY;
+            hkdfInfo = HKDF_INFO_WITHOUT_PUBLIC_KEY;
+        } else {
+            senderKeyPair = genKeyPair();
+            dhSecret = dhComputeSecret(senderKeyPair.getPrivate(), theirPublicKey);
+            hkdfInfo = HKDF_INFO_WITH_PUBLIC_KEY;
+        }
+
+        byte[] randNonce = genRandomNonce();
+        byte[] keyingMaterial = ArrayUtils.concat(dhSecret, sharedSecret);
+        SecretKey encryptionKey = hkdfDeriveKey(keyingMaterial, HKDF_SALT, hkdfInfo);
+        byte[] ciphertext = aesGcmEncrypt(encryptionKey, randNonce, payload, header);
+        if (senderKeyPair == null) {
+            return ArrayUtils.concat(VERSION, randNonce, ciphertext);
+        } else {
+            return ArrayUtils.concat(
+                    VERSION, encodePublicKey(senderKeyPair.getPublic()), randNonce, ciphertext);
+        }
+    }
+
+    /**
+     * Decrypts {@code encryptedPayload} by using {@code ourPrivateKey} and/or {@code sharedSecret}.
+     * At least one of {@code ourPrivateKey} and {@code sharedSecret} must be non-null, and an empty
+     * {@code sharedSecret} is equivalent to null.
+     *
+     * <p>Note that {@code header} should be the same data used for {@link #encrypt}, which is
+     * authenticated (but not encrypted) together with {@code payload}; otherwise, an {@code
+     * AEADBadTagException} will be thrown.
+     *
+     * @param ourPrivateKey the recipient's private key, or null if the payload was encrypted only
+     *     with the shared secret
+     * @param sharedSecret the secret shared between the sender and the recipient, or null if the
+     *     payload was encrypted only with the recipient's public key
+     * @param header the data that was authenticated with the original payload but not encrypted, or
+     *     null if the data is empty
+     * @param encryptedPayload the data to be decrypted
+     * @return the original payload that was encrypted
+     * @throws NoSuchAlgorithmException if any underlying crypto algorithm is not supported
+     * @throws InvalidKeyException if the provided key is invalid for underlying crypto algorithms
+     * @throws AEADBadTagException if the authentication tag contained in {@code encryptedPayload}
+     *     cannot be validated, or if the payload is not a valid SecureBox V2 payload.
+     * @hide
+     */
+    public static byte[] decrypt(
+            @Nullable PrivateKey ourPrivateKey,
+            @Nullable byte[] sharedSecret,
+            @Nullable byte[] header,
+            byte[] encryptedPayload)
+            throws NoSuchAlgorithmException, InvalidKeyException, AEADBadTagException {
+        sharedSecret = emptyByteArrayIfNull(sharedSecret);
+        if (ourPrivateKey == null && sharedSecret.length == 0) {
+            throw new IllegalArgumentException("Both the private key and shared secret are empty");
+        }
+        header = emptyByteArrayIfNull(header);
+        if (encryptedPayload == null) {
+            throw new NullPointerException("Encrypted payload must not be null.");
+        }
+
+        ByteBuffer ciphertextBuffer = ByteBuffer.wrap(encryptedPayload);
+        byte[] version = readEncryptedPayload(ciphertextBuffer, VERSION.length);
+        if (!Arrays.equals(version, VERSION)) {
+            throw new AEADBadTagException("The payload was not encrypted by SecureBox v2");
+        }
+
+        byte[] senderPublicKeyBytes;
+        byte[] dhSecret;
+        byte[] hkdfInfo;
+        if (ourPrivateKey == null) {
+            dhSecret = EMPTY_BYTE_ARRAY;
+            hkdfInfo = HKDF_INFO_WITHOUT_PUBLIC_KEY;
+        } else {
+            senderPublicKeyBytes = readEncryptedPayload(ciphertextBuffer, EC_PUBLIC_KEY_LEN_BYTES);
+            dhSecret = dhComputeSecret(ourPrivateKey, decodePublicKey(senderPublicKeyBytes));
+            hkdfInfo = HKDF_INFO_WITH_PUBLIC_KEY;
+        }
+
+        byte[] randNonce = readEncryptedPayload(ciphertextBuffer, GCM_NONCE_LEN_BYTES);
+        byte[] ciphertext = readEncryptedPayload(ciphertextBuffer, ciphertextBuffer.remaining());
+        byte[] keyingMaterial = ArrayUtils.concat(dhSecret, sharedSecret);
+        SecretKey decryptionKey = hkdfDeriveKey(keyingMaterial, HKDF_SALT, hkdfInfo);
+        return aesGcmDecrypt(decryptionKey, randNonce, ciphertext, header);
+    }
+
+    private static byte[] readEncryptedPayload(ByteBuffer buffer, int length)
+            throws AEADBadTagException {
+        byte[] output = new byte[length];
+        try {
+            buffer.get(output);
+        } catch (BufferUnderflowException ex) {
+            throw new AEADBadTagException("The encrypted payload is too short");
+        }
+        return output;
+    }
+
+    private static byte[] dhComputeSecret(PrivateKey ourPrivateKey, PublicKey theirPublicKey)
+            throws NoSuchAlgorithmException, InvalidKeyException {
+        KeyAgreement agreement = KeyAgreement.getInstance(KA_ALG);
+        try {
+            agreement.init(ourPrivateKey);
+        } catch (RuntimeException ex) {
+            // Rethrow the RuntimeException as InvalidKeyException
+            throw new InvalidKeyException(ex);
+        }
+        agreement.doPhase(theirPublicKey, /*lastPhase=*/ true);
+        return agreement.generateSecret();
+    }
+
+    /** Derives a 128-bit AES key. */
+    private static SecretKey hkdfDeriveKey(byte[] secret, byte[] salt, byte[] info)
+            throws NoSuchAlgorithmException {
+        Mac mac = Mac.getInstance(MAC_ALG);
+        try {
+            mac.init(new SecretKeySpec(salt, MAC_ALG));
+        } catch (InvalidKeyException ex) {
+            // This should never happen
+            throw new RuntimeException(ex);
+        }
+        byte[] pseudorandomKey = mac.doFinal(secret);
+
+        try {
+            mac.init(new SecretKeySpec(pseudorandomKey, MAC_ALG));
+        } catch (InvalidKeyException ex) {
+            // This should never happen
+            throw new RuntimeException(ex);
+        }
+        mac.update(info);
+        // Hashing just one block will yield 256 bits, which is enough to construct the AES key
+        byte[] hkdfOutput = mac.doFinal(CONSTANT_01);
+
+        return new SecretKeySpec(Arrays.copyOf(hkdfOutput, GCM_KEY_LEN_BYTES), CIPHER_ALG);
+    }
+
+    private static byte[] aesGcmEncrypt(SecretKey key, byte[] nonce, byte[] plaintext, byte[] aad)
+            throws NoSuchAlgorithmException, InvalidKeyException {
+        try {
+            return aesGcmInternal(AesGcmOperation.ENCRYPT, key, nonce, plaintext, aad);
+        } catch (AEADBadTagException ex) {
+            // This should never happen
+            throw new RuntimeException(ex);
+        }
+    }
+
+    private static byte[] aesGcmDecrypt(SecretKey key, byte[] nonce, byte[] ciphertext, byte[] aad)
+            throws NoSuchAlgorithmException, InvalidKeyException, AEADBadTagException {
+        return aesGcmInternal(AesGcmOperation.DECRYPT, key, nonce, ciphertext, aad);
+    }
+
+    private static byte[] aesGcmInternal(
+            AesGcmOperation operation, SecretKey key, byte[] nonce, byte[] text, byte[] aad)
+            throws NoSuchAlgorithmException, InvalidKeyException, AEADBadTagException {
+        Cipher cipher;
+        try {
+            cipher = Cipher.getInstance(ENC_ALG);
+        } catch (NoSuchPaddingException ex) {
+            // This should never happen because AES-GCM doesn't use padding
+            throw new RuntimeException(ex);
+        }
+        GCMParameterSpec spec = new GCMParameterSpec(GCM_TAG_LEN_BYTES * 8, nonce);
+        try {
+            if (operation == AesGcmOperation.DECRYPT) {
+                cipher.init(Cipher.DECRYPT_MODE, key, spec);
+            } else {
+                cipher.init(Cipher.ENCRYPT_MODE, key, spec);
+            }
+        } catch (InvalidAlgorithmParameterException ex) {
+            // This should never happen
+            throw new RuntimeException(ex);
+        }
+        try {
+            cipher.updateAAD(aad);
+            return cipher.doFinal(text);
+        } catch (AEADBadTagException ex) {
+            // Catch and rethrow AEADBadTagException first because it's a subclass of
+            // BadPaddingException
+            throw ex;
+        } catch (IllegalBlockSizeException | BadPaddingException ex) {
+            // This should never happen because AES-GCM can handle inputs of any length without
+            // padding
+            throw new RuntimeException(ex);
+        }
+    }
+
+    /**
+     * Encodes public key in format expected by the secure hardware module. This is used as part
+     * of the vault params.
+     *
+     * @param publicKey The public key.
+     * @return The key packed into a 65-byte array.
+     */
+    public static byte[] encodePublicKey(PublicKey publicKey) {
+        ECPoint point = ((ECPublicKey) publicKey).getW();
+        byte[] x = point.getAffineX().toByteArray();
+        byte[] y = point.getAffineY().toByteArray();
+
+        byte[] output = new byte[EC_PUBLIC_KEY_LEN_BYTES];
+        // The order of arraycopy() is important, because the coordinates may have a one-byte
+        // leading 0 for the sign bit of two's complement form
+        System.arraycopy(y, 0, output, EC_PUBLIC_KEY_LEN_BYTES - y.length, y.length);
+        System.arraycopy(x, 0, output, 1 + EC_COORDINATE_LEN_BYTES - x.length, x.length);
+        output[0] = EC_PUBLIC_KEY_PREFIX;
+        return output;
+    }
+
+    /**
+     * Decodes byte[] encoded public key.
+     *
+     * @param keyBytes encoded public key
+     * @return the public key
+     */
+    public static PublicKey decodePublicKey(byte[] keyBytes)
+            throws NoSuchAlgorithmException, InvalidKeyException {
+        BigInteger x =
+                new BigInteger(
+                        /*signum=*/ 1,
+                        Arrays.copyOfRange(keyBytes, 1, 1 + EC_COORDINATE_LEN_BYTES));
+        BigInteger y =
+                new BigInteger(
+                        /*signum=*/ 1,
+                        Arrays.copyOfRange(
+                                keyBytes, 1 + EC_COORDINATE_LEN_BYTES, EC_PUBLIC_KEY_LEN_BYTES));
+
+        // Checks if the point is indeed on the P-256 curve for security considerations
+        validateEcPoint(x, y);
+
+        KeyFactory keyFactory = KeyFactory.getInstance(EC_ALG);
+        try {
+            return keyFactory.generatePublic(new ECPublicKeySpec(new ECPoint(x, y), EC_PARAM_SPEC));
+        } catch (InvalidKeySpecException ex) {
+            // This should never happen
+            throw new RuntimeException(ex);
+        }
+    }
+
+    private static void validateEcPoint(BigInteger x, BigInteger y) throws InvalidKeyException {
+        if (x.compareTo(EC_PARAM_P) >= 0
+                || y.compareTo(EC_PARAM_P) >= 0
+                || x.signum() == -1
+                || y.signum() == -1) {
+            throw new InvalidKeyException("Point lies outside of the expected curve");
+        }
+
+        // Points on the curve satisfy y^2 = x^3 + ax + b (mod p)
+        BigInteger lhs = y.modPow(BIG_INT_02, EC_PARAM_P);
+        BigInteger rhs =
+                x.modPow(BIG_INT_02, EC_PARAM_P) // x^2
+                        .add(EC_PARAM_A) // x^2 + a
+                        .mod(EC_PARAM_P) // This will speed up the next multiplication
+                        .multiply(x) // (x^2 + a) * x = x^3 + ax
+                        .add(EC_PARAM_B) // x^3 + ax + b
+                        .mod(EC_PARAM_P);
+        if (!lhs.equals(rhs)) {
+            throw new InvalidKeyException("Point lies outside of the expected curve");
+        }
+    }
+
+    private static byte[] genRandomNonce() throws NoSuchAlgorithmException {
+        byte[] nonce = new byte[GCM_NONCE_LEN_BYTES];
+        new SecureRandom().nextBytes(nonce);
+        return nonce;
+    }
+
+    private static byte[] emptyByteArrayIfNull(@Nullable byte[] input) {
+        return input == null ? EMPTY_BYTE_ARRAY : input;
+    }
+}