Get SHA1 digital footprint from android application based on its package name.

gistfile1.java

public static final String tag = "Security";
  private static final boolean debug = true;
	
	/**
	 * Gets an application's SHA1 footprint(s) from their digital signature(s).
	 * @param packageName is the package name of the application you want to retrieve
	 * the SHA1 footprints from.
	 * @return a list of SHA1 footprints or null.
	 */
	private ArrayList<String> getFootprints(String packageName) {
		Signature[] sigs = null;
		ArrayList<String> footprints = new ArrayList<String>();
		
		// Get the application's digital signatures.
		try {
			sigs = getBaseContext().getPackageManager().getPackageInfo(packageName, PackageManager.GET_SIGNATURES).signatures;
		} catch(Exception ex) {
			if(debug) {
				Log.e(tag, ex.toString());
			}
		}
		
		// If there was an error then return nothing.
		if(sigs == null) {
			return null;
		}
		
		// Extract the SHA1 footprint from each signature.
		for(Signature sig : sigs) {
			byte[] hexBytes = sig.toByteArray();			    
			MessageDigest digest = null;
			
			// Get the SHA1 footprint
			try {
				digest = MessageDigest.getInstance("SHA1");	
			} catch(Exception ex) {
				if(debug) {
					Log.e(tag, ex.toString());
				}
			}
 
			// Check for a valid digest
			if(digest == null) {
				return null;
			}
			
			byte[] sha1digest = new byte[0];
			if(digest != null)  {
				sha1digest = digest.digest(hexBytes);
				StringBuilder sb = new StringBuilder();
				for(int i = 0; i < sha1digest.length; ++i)  {
					sb.append((Integer.toHexString((sha1digest[i] & 0xFF) | 0x100)).substring(1, 3));
				}
				footprints.add(sb.toString());
			}
		}
		
		return footprints;
	}