diff -r 000000000000 -r 6474c204b198 mobile/android/base/browserid/RSACryptoImplementation.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/browserid/RSACryptoImplementation.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,186 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.browserid;
+
+import java.math.BigInteger;
+import java.security.GeneralSecurityException;
+import java.security.KeyFactory;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.NoSuchAlgorithmException;
+import java.security.Signature;
+import java.security.interfaces.RSAPrivateKey;
+import java.security.interfaces.RSAPublicKey;
+import java.security.spec.InvalidKeySpecException;
+import java.security.spec.KeySpec;
+import java.security.spec.RSAPrivateKeySpec;
+import java.security.spec.RSAPublicKeySpec;
+
+import org.mozilla.gecko.sync.ExtendedJSONObject;
+import org.mozilla.gecko.sync.NonObjectJSONException;
+
+public class RSACryptoImplementation {
+  public static final String SIGNATURE_ALGORITHM = "SHA256withRSA";
+
+  /**
+   * Parameters are serialized as decimal strings. Hex-versus-decimal was
+   * reverse-engineered from what the Persona public verifier accepted. We
+   * expect to follow the JOSE/JWT spec as it solidifies, and that will probably
+   * mean unifying this base.
+   */
+  protected static final int SERIALIZATION_BASE = 10;
+
+  protected static class RSAVerifyingPublicKey implements VerifyingPublicKey {
+    protected final RSAPublicKey publicKey;
+
+    public RSAVerifyingPublicKey(RSAPublicKey publicKey) {
+      this.publicKey = publicKey;
+    }
+
+    /**
+     * Serialize to a JSON object.
+     * <p>
+     * Parameters are serialized as decimal strings. Hex-versus-decimal was
+     * reverse-engineered from what the Persona public verifier accepted.
+     */
+    @Override
+    public ExtendedJSONObject toJSONObject() {
+      ExtendedJSONObject o = new ExtendedJSONObject();
+      o.put("algorithm", "RS");
+      o.put("n", publicKey.getModulus().toString(SERIALIZATION_BASE));
+      o.put("e", publicKey.getPublicExponent().toString(SERIALIZATION_BASE));
+      return o;
+    }
+
+    @Override
+    public boolean verifyMessage(byte[] bytes, byte[] signature)
+        throws GeneralSecurityException {
+      final Signature signer = Signature.getInstance(SIGNATURE_ALGORITHM);
+      signer.initVerify(publicKey);
+      signer.update(bytes);
+      return signer.verify(signature);
+    }
+  }
+
+  protected static class RSASigningPrivateKey implements SigningPrivateKey {
+    protected final RSAPrivateKey privateKey;
+
+    public RSASigningPrivateKey(RSAPrivateKey privateKey) {
+      this.privateKey = privateKey;
+    }
+
+    @Override
+    public String getAlgorithm() {
+      return "RS" + (privateKey.getModulus().bitLength() + 7)/8;
+    }
+
+    /**
+     * Serialize to a JSON object.
+     * <p>
+     * Parameters are serialized as decimal strings. Hex-versus-decimal was
+     * reverse-engineered from what the Persona public verifier accepted.
+     */
+    @Override
+    public ExtendedJSONObject toJSONObject() {
+      ExtendedJSONObject o = new ExtendedJSONObject();
+      o.put("algorithm", "RS");
+      o.put("n", privateKey.getModulus().toString(SERIALIZATION_BASE));
+      o.put("d", privateKey.getPrivateExponent().toString(SERIALIZATION_BASE));
+      return o;
+    }
+
+    @Override
+    public byte[] signMessage(byte[] bytes)
+        throws GeneralSecurityException {
+      final Signature signer = Signature.getInstance(SIGNATURE_ALGORITHM);
+      signer.initSign(privateKey);
+      signer.update(bytes);
+      return signer.sign();
+    }
+  }
+
+  public static BrowserIDKeyPair generateKeyPair(final int keysize) throws NoSuchAlgorithmException {
+    final KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
+    keyPairGenerator.initialize(keysize);
+    final KeyPair keyPair = keyPairGenerator.generateKeyPair();
+    RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
+    RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
+    return new BrowserIDKeyPair(new RSASigningPrivateKey(privateKey), new RSAVerifyingPublicKey(publicKey));
+  }
+
+  public static SigningPrivateKey createPrivateKey(BigInteger n, BigInteger d) throws NoSuchAlgorithmException, InvalidKeySpecException {
+    if (n == null) {
+      throw new IllegalArgumentException("n must not be null");
+    }
+    if (d == null) {
+      throw new IllegalArgumentException("d must not be null");
+    }
+    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
+    KeySpec keySpec = new RSAPrivateKeySpec(n, d);
+    RSAPrivateKey privateKey = (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
+    return new RSASigningPrivateKey(privateKey);
+  }
+
+  public static VerifyingPublicKey createPublicKey(BigInteger n, BigInteger e) throws NoSuchAlgorithmException, InvalidKeySpecException {
+    if (n == null) {
+      throw new IllegalArgumentException("n must not be null");
+    }
+    if (e == null) {
+      throw new IllegalArgumentException("e must not be null");
+    }
+    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
+    KeySpec keySpec = new RSAPublicKeySpec(n, e);
+    RSAPublicKey publicKey = (RSAPublicKey) keyFactory.generatePublic(keySpec);
+    return new RSAVerifyingPublicKey(publicKey);
+  }
+
+  public static SigningPrivateKey createPrivateKey(ExtendedJSONObject o) throws InvalidKeySpecException, NoSuchAlgorithmException {
+    String algorithm = o.getString("algorithm");
+    if (!"RS".equals(algorithm)) {
+      throw new InvalidKeySpecException("algorithm must equal RS, was " + algorithm);
+    }
+    try {
+      BigInteger n = new BigInteger(o.getString("n"), SERIALIZATION_BASE);
+      BigInteger d = new BigInteger(o.getString("d"), SERIALIZATION_BASE);
+      return createPrivateKey(n, d);
+    } catch (NullPointerException e) {
+      throw new InvalidKeySpecException("n and d must be integers encoded as strings, base " + SERIALIZATION_BASE);
+    } catch (NumberFormatException e) {
+      throw new InvalidKeySpecException("n and d must be integers encoded as strings, base " + SERIALIZATION_BASE);
+    }
+  }
+
+  public static VerifyingPublicKey createPublicKey(ExtendedJSONObject o) throws InvalidKeySpecException, NoSuchAlgorithmException {
+    String algorithm = o.getString("algorithm");
+    if (!"RS".equals(algorithm)) {
+      throw new InvalidKeySpecException("algorithm must equal RS, was " + algorithm);
+    }
+    try {
+      BigInteger n = new BigInteger(o.getString("n"), SERIALIZATION_BASE);
+      BigInteger e = new BigInteger(o.getString("e"), SERIALIZATION_BASE);
+      return createPublicKey(n, e);
+    } catch (NullPointerException e) {
+      throw new InvalidKeySpecException("n and e must be integers encoded as strings, base " + SERIALIZATION_BASE);
+    } catch (NumberFormatException e) {
+      throw new InvalidKeySpecException("n and e must be integers encoded as strings, base " + SERIALIZATION_BASE);
+    }
+  }
+
+  public static BrowserIDKeyPair fromJSONObject(ExtendedJSONObject o) throws InvalidKeySpecException, NoSuchAlgorithmException {
+    try {
+      ExtendedJSONObject privateKey = o.getObject(BrowserIDKeyPair.JSON_KEY_PRIVATEKEY);
+      ExtendedJSONObject publicKey = o.getObject(BrowserIDKeyPair.JSON_KEY_PUBLICKEY);
+      if (privateKey == null) {
+        throw new InvalidKeySpecException("privateKey must not be null");
+      }
+      if (publicKey == null) {
+        throw new InvalidKeySpecException("publicKey must not be null");
+      }
+      return new BrowserIDKeyPair(createPrivateKey(privateKey), createPublicKey(publicKey));
+    } catch (NonObjectJSONException e) {
+      throw new InvalidKeySpecException("privateKey and publicKey must be JSON objects");
+    }
+  }
+}