Android-Java RSA decrypt

Question

i need to create a public key for RSA algorithm from a binary string.

My code is:

String pubKey = "tihq/Gk3OUs5NzP+XTRKXBwSxHtB0TWn0RREcpXEtp316tyD9DzKaIbdKexb/mRr";

byte[] keyBytes = Base64.decode(pubKey,Base64.DEFAULT);
//test if is correct: ok
Log.d("response keyBytes",new String(Base64.encode(keyBytes,Base64.DEFAULT)));

KeyFactory keyFactory = KeyFactory.getInstance("RSA");      
X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);

RSAPublicKey publicKey = (RSAPublicKey) keyFactory.generatePublic(spec);
//PublicKey publicKey = (PublicKey) keyFactory.generatePublic(spec);

But i have this error:

java.security.spec.InvalidKeySpecException: java.lang.RuntimeException: error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag

invisibleProgrammer · Accepted Answer · 2014-09-30 14:53:11Z

2

SOLVED. The problem is that i have modulus and exponent and so i must to do this:

String pubKey = "tihq/Gk3OUs5NzP+XTRKXBwSxHtB0TWn0RREcpXEtp316tyD9DzKaIbdKexb/mRr"; //64 caratteri
String exponent = "AQAB";

byte[] keyBytes = Base64.decode(pubKey,Base64.DEFAULT);
byte[] exponentByte = Base64.decode(exponent,Base64.DEFAULT);

KeyFactory keyFactory = KeyFactory.getInstance("RSA");

RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger(keyBytes), new BigInteger(exponentByte));
RSAPublicKey publicKey = (RSAPublicKey) keyFactory.generatePublic(pubKeySpec);

answered Sep 30, 2014 at 14:53

invisibleProgrammer

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