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/*
* Copyright (C) 2008 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.dumpkey;
import java.io.FileInputStream;
import java.math.BigInteger;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.security.KeyStore;
import java.security.Key;
import java.security.PublicKey;
import java.security.interfaces.RSAPublicKey;
/**
* Command line tool to extract RSA public keys from X.509 certificates
* and output source code with data initializers for the keys.
* @hide
*/
class DumpPublicKey {
/**
* @param key to perform sanity checks on
* @return version number of key. Supported versions are:
* 1: 2048-bit RSA key with e=3 and SHA-1 hash
* 2: 2048-bit RSA key with e=65537 and SHA-1 hash
* 3: 2048-bit RSA key with e=3 and SHA-256 hash
* 4: 2048-bit RSA key with e=65537 and SHA-256 hash
* @throws Exception if the key has the wrong size or public exponent
*/
static int check(RSAPublicKey key, boolean useSHA256) throws Exception {
BigInteger pubexp = key.getPublicExponent();
BigInteger modulus = key.getModulus();
int version;
if (pubexp.equals(BigInteger.valueOf(3))) {
version = useSHA256 ? 3 : 1;
} else if (pubexp.equals(BigInteger.valueOf(65537))) {
version = useSHA256 ? 4 : 2;
} else {
throw new Exception("Public exponent should be 3 or 65537 but is " +
pubexp.toString(10) + ".");
}
if (modulus.bitLength() != 2048) {
throw new Exception("Modulus should be 2048 bits long but is " +
modulus.bitLength() + " bits.");
}
return version;
}
/**
* @param key to output
* @return a String representing this public key. If the key is a
* version 1 key, the string will be a C initializer; this is
* not true for newer key versions.
*/
static String print(RSAPublicKey key, boolean useSHA256) throws Exception {
int version = check(key, useSHA256);
BigInteger N = key.getModulus();
StringBuilder result = new StringBuilder();
int nwords = N.bitLength() / 32; // # of 32 bit integers in modulus
if (version > 1) {
result.append("v");
result.append(Integer.toString(version));
result.append(" ");
}
result.append("{");
result.append(nwords);
BigInteger B = BigInteger.valueOf(0x100000000L); // 2^32
BigInteger N0inv = B.subtract(N.modInverse(B)); // -1 / N[0] mod 2^32
result.append(",0x");
result.append(N0inv.toString(16));
BigInteger R = BigInteger.valueOf(2).pow(N.bitLength());
BigInteger RR = R.multiply(R).mod(N); // 2^4096 mod N
// Write out modulus as little endian array of integers.
result.append(",{");
for (int i = 0; i < nwords; ++i) {
long n = N.mod(B).longValue();
result.append(n);
if (i != nwords - 1) {
result.append(",");
}
N = N.divide(B);
}
result.append("}");
// Write R^2 as little endian array of integers.
result.append(",{");
for (int i = 0; i < nwords; ++i) {
long rr = RR.mod(B).longValue();
result.append(rr);
if (i != nwords - 1) {
result.append(",");
}
RR = RR.divide(B);
}
result.append("}");
result.append("}");
return result.toString();
}
public static void main(String[] args) {
if (args.length < 1) {
System.err.println("Usage: DumpPublicKey certfile ... > source.c");
System.exit(1);
}
try {
for (int i = 0; i < args.length; i++) {
FileInputStream input = new FileInputStream(args[i]);
CertificateFactory cf = CertificateFactory.getInstance("X.509");
X509Certificate cert = (X509Certificate) cf.generateCertificate(input);
boolean useSHA256 = false;
String sigAlg = cert.getSigAlgName();
if ("SHA1withRSA".equals(sigAlg) || "MD5withRSA".equals(sigAlg)) {
// SignApk has historically accepted "MD5withRSA"
// certificates, but treated them as "SHA1withRSA"
// anyway. Continue to do so for backwards
// compatibility.
useSHA256 = false;
} else if ("SHA256withRSA".equals(sigAlg)) {
useSHA256 = true;
} else {
System.err.println(args[i] + ": unsupported signature algorithm \"" +
sigAlg + "\"");
System.exit(1);
}
RSAPublicKey key = (RSAPublicKey) (cert.getPublicKey());
check(key, useSHA256);
System.out.print(print(key, useSHA256));
System.out.println(i < args.length - 1 ? "," : "");
}
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
System.exit(0);
}
}
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