Сначала вам нужно сгенерировать открытый ключ из предоставленного вами формата pem, вот мой метод для этого:
/**
*
* @param PEMString -A file/string in .pem format with a generated RSA key (with "des3", using "openssl genrsa".)
* @param isFilePath - If it's a file path or a string
* @return java.security.PublicKey
* @throws IOException -No key found
* @throws NoSuchAlgorithmException
* @throws InvalidKeySpecException
*
* @author hsigmond
*/
private static PublicKey getPublicKeyFromPemFormat(String PEMString,
boolean isFilePath) throws IOException, NoSuchAlgorithmException,
InvalidKeySpecException {
BufferedReader pemReader = null;
if (isFilePath) {
pemReader = new BufferedReader(new InputStreamReader(
new FileInputStream(PEMString)));
} else {
pemReader = new BufferedReader(new InputStreamReader(
new ByteArrayInputStream(PEMString.getBytes("UTF-8"))));
}
StringBuffer content = new StringBuffer();
String line = null;
while ((line = pemReader.readLine()) != null) {
if (line.indexOf("-----BEGIN PUBLIC KEY-----") != -1) {
while ((line = pemReader.readLine()) != null) {
if (line.indexOf("-----END PUBLIC KEY") != -1) {
break;
}
content.append(line.trim());
}
break;
}
}
if (line == null) {
throw new IOException("PUBLIC KEY" + " not found");
}
Log.i("PUBLIC KEY: ", "PEM content = : " + content.toString());
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
return keyFactory.generatePublic(new X509EncodedKeySpec(Base64.decode(content.toString(), Base64.DEFAULT)));
}
А вот как я использую его для чтения (декодирования) подписанного контентас открытым ключом.
/**
*
* @param PEMString -A file/string in .pem format with a generated RSA key (with "des3", using "openssl genrsa".)
* @param content
* @return String value of content Decoded
* @throws NoSuchAlgorithmException
* @throws InvalidKeySpecException
* @throws IOException
* @throws NoSuchProviderException
* @throws NoSuchPaddingException
* @throws InvalidKeyException
* @throws IllegalBlockSizeException
* @throws BadPaddingException
*
* @author hsigmond
*/
public static String getContentWithPublicKeyFromPemFormat(String PEMString,
String content,boolean isFilePath) throws NoSuchAlgorithmException,
InvalidKeySpecException, IOException, NoSuchProviderException,
NoSuchPaddingException, InvalidKeyException,
IllegalBlockSizeException, BadPaddingException {
PublicKey publicKey = getPublicKeyFromPemFormat(PEMString,isFilePath);
if (publicKey != null)
Log.i("PUBLIC KEY: ", "FORMAT : " + publicKey.getFormat()
+ " \ntoString : " + publicKey.toString());
byte[] contentBytes = Base64.decode(content, Base64.DEFAULT);
byte[] decoded = null;
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "BC");//BC=BouncyCastle Provider
cipher.init(Cipher.DECRYPT_MODE, publicKey);
decoded = cipher.doFinal(contentBytes);
return new String(decoded, "UTF-8");
}