从PEM BASE64编码的私钥文件中获取RSA私钥

由于缺少ASN1支持，因此解析PKCS1（在Android上仅开箱即用的PKCS8格式）键是一项繁琐的任务，但如果包含Spongy castle jar以读取DER Integers，则可以解决。

String privKeyPEM = key.replace("-----BEGIN RSA PRIVATE KEY-----n", "")    .replace("-----END RSA PRIVATE KEY-----", "");// base64 depre the databyte[] enpredPrivateKey = base64.depre(privKeyPEM, base64.DEFAULT);try {    ASN1Sequence primitive = (ASN1Sequence) ASN1Sequence        .fromByteArray(enpredPrivateKey);    Enumeration<?> e = primitive.getObjects();    BigInteger v = ((DERInteger) e.nextElement()).getValue();    int version = v.intValue();    if (version != 0 && version != 1) {        throw new IllegalArgumentException("wrong version for RSA private key");    }        BigInteger modulus = ((DERInteger) e.nextElement()).getValue();    BigInteger publicExponent = ((DERInteger) e.nextElement()).getValue();    BigInteger privateExponent = ((DERInteger) e.nextElement()).getValue();    BigInteger prime1 = ((DERInteger) e.nextElement()).getValue();    BigInteger prime2 = ((DERInteger) e.nextElement()).getValue();    BigInteger exponent1 = ((DERInteger) e.nextElement()).getValue();    BigInteger exponent2 = ((DERInteger) e.nextElement()).getValue();    BigInteger coefficient = ((DERInteger) e.nextElement()).getValue();    RSAPrivateKeySpec spec = new RSAPrivateKeySpec(modulus, privateExponent);    KeyFactory kf = KeyFactory.getInstance("RSA");    PrivateKey pk = kf.generatePrivate(spec);} catch (IOException e2) {    throw new IllegalStateException();} catch (NoSuchAlgorithmException e) {    throw new IllegalStateException(e);} catch (InvalidKeySpecException e) {    throw new IllegalStateException(e);}