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(Java) Duplicate openssl rsautl -verify -inkey pubKey.pem -pubin -in rsautl.sig -out originalFile.datDemonstrates how to duplicate this OpenSSL command: openssl rsautl -verify -inkey pubKey.pem -pubin -in rsautl.sig -out originalFile.datThe signature file contains the contents of the original data, and the original data is output to "originalFile.dat". The openssl rsautl command signs the data directly, and therefore the maximum amount of data that can signed is very small. (To sign any amount of data, use openssl dgst -sign.) The maximum amount of data that can be signed (with rsautl) is the key size minus the overhead for the padding. The overhead size depends on the padding. With OAEP padding, the overhead is 42 bytes. With the default PKCSv1.5 padding, the overhead is 11 bytes. Given a 2048-bit RSA key (256 bytes) and using PKCSv1.5 padding, the max data size that can be signed is 256 - 11 = 245 bytes.
import com.chilkatsoft.*; public class ChilkatExample { static { try { System.loadLibrary("chilkat"); } catch (UnsatisfiedLinkError e) { System.err.println("Native code library failed to load.\n" + e); System.exit(1); } } public static void main(String argv[]) { // This example requires the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. CkPublicKey pubKey = new CkPublicKey(); // Load the public key from an PEM file: boolean success = pubKey.LoadFromFile("pubKey.pem"); if (success != true) { System.out.println(pubKey.lastErrorText()); return; } // Load the signature. CkByteData sigData = new CkByteData(); success = sigData.loadFile("rsautl.sig"); if (success != true) { System.out.println("Failed to the signature file."); return; } CkRsa rsa = new CkRsa(); // Import the public key into the RSA component: success = rsa.ImportPublicKeyObj(pubKey); if (success != true) { System.out.println(rsa.lastErrorText()); return; } // OpenSSL uses big-endian... rsa.put_LittleEndian(false); CkByteData origData = new CkByteData(); success = rsa.OpenSslVerifyBytes(sigData,origData); if (success != true) { System.out.println(rsa.lastErrorText()); System.out.println("The signature was invalid."); return; } System.out.println("The signature was verified successfully."); // Save the original data extracted from the signature: success = origData.saveFile("originalFile.dat"); if (success != true) { System.out.println("Failed to save the original data file."); return; } } } |
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