title: Using Bouncy Castle to extract certificate information from android
body: <p>I am trying to use bouncy castle to read the content of CERT.RSA in an Android apk file.</p>
  
  <p>By using : <code>openssl pkcs7 -inform DER -in CERT.RSA -noout -print_certs -text</code></p>
  
  <p>I am get the following, which seems correct :</p>
  
  <pre><code>Certificate:
  Data:
      Version: 3 (0x2)
      Serial Number:
          93:6e:ac:be:07:f2:01:df
      Signature Algorithm: sha1WithRSAEncryption
      Issuer: C=US, ST=California, L=Mountain View, O=Android, OU=Android, CN=Android/emailAddress=android@android.com
      Validity
          Not Before: Feb 29 01:33:46 2008 GMT
          Not After : Jul 17 01:33:46 2035 GMT
      Subject: C=US, ST=California, L=Mountain View, O=Android, OU=Android, CN=Android/emailAddress=android@android.com
      Subject Public Key Info:
          Public Key Algorithm: rsaEncryption
              Public-Key: (2048 bit)
              Modulus:
                  00:d6:93:19:04:de:c6:0b:24:b1:ed:c7:62:e0:d9:
                  d8:25:3e:3e:cd:6c:eb:1d:e2:ff:06:8c:a8:e8:bc:
                  a8:cd:6b:d3:78:6e:a7:0a:a7:6c:e6:0e:bb:0f:99:
                  35:59:ff:d9:3e:77:a9:43:e7:e8:3d:4b:64:b8:e4:
                  fe:a2:d3:e6:56:f1:e2:67:a8:1b:bf:b2:30:b5:78:
                  c2:04:43:be:4c:72:18:b8:46:f5:21:15:86:f0:38:
                  a1:4e:89:c2:be:38:7f:8e:be:cf:8f:ca:c3:da:1e:
                  e3:30:c9:ea:93:d0:a7:c3:dc:4a:f3:50:22:0d:50:
                  08:07:32:e0:80:97:17:ee:6a:05:33:59:e6:a6:94:
                  ec:2c:b3:f2:84:a0:a4:66:c8:7a:94:d8:3b:31:09:
                  3a:67:37:2e:2f:64:12:c0:6e:6d:42:f1:58:18:df:
                  fe:03:81:cc:0c:d4:44:da:6c:dd:c3:b8:24:58:19:
                  48:01:b3:25:64:13:4f:bf:de:98:c9:28:77:48:db:
                  f5:67:6a:54:0d:81:54:c8:bb:ca:07:b9:e2:47:55:
                  33:11:c4:6b:9a:f7:6f:de:ec:cc:8e:69:e7:c8:a2:
                  d0:8e:78:26:20:94:3f:99:72:7d:3c:04:fe:72:99:
                  1d:99:df:9b:ae:38:a0:b2:17:7f:a3:1d:5b:6a:fe:
                  e9:1f
              Exponent: 3 (0x3)
      X509v3 extensions:
          X509v3 Subject Key Identifier: 
              48:59:00:56:3D:27:2C:46:AE:11:86:05:A4:74:19:AC:09:CA:8C:11
          X509v3 Authority Key Identifier: 
              keyid:48:59:00:56:3D:27:2C:46:AE:11:86:05:A4:74:19:AC:09:CA:8C:11
              DirName:/C=US/ST=California/L=Mountain View/O=Android/OU=Android/CN=Android/emailAddress=android@android.com
              serial:93:6E:AC:BE:07:F2:01:DF
  
          X509v3 Basic Constraints: 
              CA:TRUE
  Signature Algorithm: sha1WithRSAEncryption
      7a:af:96:8c:eb:50:c4:41:05:51:18:d0:da:ab:af:01:5b:8a:
      76:5a:27:a7:15:a2:c2:b4:4f:22:14:15:ff:da:ce:03:09:5a:
      bf:a4:2d:f7:07:08:72:6c:20:69:e5:c3:6e:dd:ae:04:00:be:
      29:45:2c:08:4b:c2:7e:b6:a1:7e:ac:9d:be:18:2c:20:4e:b1:
      53:11:f4:55:d8:24:b6:56:db:e4:dc:22:40:91:2d:75:86:fe:
      88:95:1d:01:a8:fe:b5:ae:5a:42:60:53:5d:f8:34:31:05:24:
      22:46:8c:36:e2:2c:2a:5e:f9:94:d6:1d:d7:30:6a:e4:c9:f6:
      95:1b:a3:c1:2f:1d:19:14:dd:c6:1f:1a:62:da:2d:f8:27:f6:
      03:fe:a5:60:3b:2c:54:0d:bd:7c:01:9c:36:ba:b2:9a:42:71:
      c1:17:df:52:3c:db:c5:f3:81:7a:49:e0:ef:a6:0c:bd:7f:74:
      17:7e:7a:4f:19:3d:43:f4:22:07:72:66:6e:4c:4d:83:e1:bd:
      5a:86:08:7c:f3:4f:2d:ec:21:e2:45:ca:6c:2b:b0:16:e6:83:
      63:80:50:d2:c4:30:ee:a7:c2:6a:1c:49:d3:76:0a:58:ab:7f:
      1a:82:cc:93:8b:48:31:38:43:24:bd:04:01:fa:12:16:3a:50:
      57:0e:68:4d
  </code></pre>
  
  <p>But I don't get the public key modulus and the other necessary stuff when I'm using Bouncy Castle. The pubkey is just null. I guess I made some mistake in the code, but it is weird that I get everything I want, except for the public key.</p>
  
  <pre><code>X509CertParser certParser = new X509CertParser();
  FileInputStream stream;
  X509CertificateObject cert= null;
  try {
  stream = new FileInputStream("CERT.RSA");
      certParser.engineInit(stream);
      cert =  (X509CertificateObject) certParser.engineRead();
      stream.close();
  
      if(cert.getPublicKey()==null)System.out.println("NULL");
  
      } catch (FileNotFoundException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      } catch (IOException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      }
  </code></pre>
  
  <p>This code prints NULL, while the openssl call tells me the modulus etc.</p>
  
  <p>What should I do to get the pubkey in Java ? (maybe it is possible to use android sdk or something else to get the data instead of bouncy castle)</p>
  
  <p>Edit:</p>
  
  <p>I forgot to mention that i already tried David Grants code, which gives me the error message, that the DerInputStream is too big:</p>
  
  <pre><code>java.security.cert.CertificateException: Unable to initialize, java.io.IOException: DerInputStream.getLength(): lengthTag=127, too big.
  at sun.security.x509.X509CertImpl.&lt;init&gt;(X509CertImpl.java:199)
  at sun.security.provider.X509Factory.engineGenerateCertificate(X509Factory.java:107)
  at java.security.cert.CertificateFactory.generateCertificate(CertificateFactory.java:322)
  </code></pre>