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DumpPublicKey.javaAPI DocAndroid 1.5 API4204Wed May 06 22:43:10 BST 2009com.android.dumpkey

DumpPublicKey

public class DumpPublicKey extends Object
Command line tool to extract RSA public keys from X.509 certificates and output source code with data initializers for the keys.
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Fields Summary
Constructors Summary
Methods Summary
static voidcheck(java.security.interfaces.RSAPublicKey key)

param
key to perform sanity checks on
throws
Exception if the key has the wrong size or public exponent

        BigInteger pubexp = key.getPublicExponent();
        BigInteger modulus = key.getModulus();

        if (!pubexp.equals(BigInteger.valueOf(3)))
                throw new Exception("Public exponent should be 3 but is " +
                        pubexp.toString(10) + ".");

        if (modulus.bitLength() != 2048)
             throw new Exception("Modulus should be 2048 bits long but is " +
                        modulus.bitLength() + " bits.");
public static voidmain(java.lang.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");
                Certificate cert = cf.generateCertificate(input);
                RSAPublicKey key = (RSAPublicKey) (cert.getPublicKey());
                check(key);
                System.out.print(print(key));
                System.out.println(i < args.length - 1 ? "," : "");
            }
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }
        System.exit(0);
static java.lang.Stringprint(java.security.interfaces.RSAPublicKey key)

param
key to output
return
a C initializer representing this public key.

        check(key);

        BigInteger N = key.getModulus();

        StringBuilder result = new StringBuilder();

        int nwords = N.bitLength() / 32;    // # of 32 bit integers in modulus

        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) {
            int n = N.mod(B).intValue();
            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) {
            int rr = RR.mod(B).intValue();
            result.append(rr);

            if (i != nwords - 1) {
                result.append(",");
            }

            RR = RR.divide(B);
        }
        result.append("}");

        result.append("}");
        return result.toString();