Generating and Verifying Signatures |
NextVerSig
needs to import the encoded public key bytes from the file specified as the first command line argument, and convert them to aPublicKey
. APublicKey
is needed because that is what theSignature
initVerify
method requires in order to initialize theSignature
object for verification.First, read in the encoded public key bytes:
Now the byte arrayFileInputStream keyfis = new FileInputStream(args[0]); byte[] encKey = new byte[keyfis.available()]; keyfis.read(encKey); keyfis.close();encKey
contains the encoded public key bytes.You can use a
KeyFactory
in order to instantiate a DSA public key from its encoding. TheKeyFactory
class provides conversions between opaque keys (of typeKey
) and key specifications, which are transparent representations of the underlying key material. With an opaque key, you can obtain the algorithm name, format name, and encoded key bytes, but not the key material, which, for example, may consist of the key itself and the algorithm parameters used to calculate the key. (Note: aPublicKey
is aKey
, since it extendsKey
.)So, first you need a key specification. You can obtain one via the following, assuming the key was encoded according to the X.509 standard (which is the case, for example, if the key was generated with the built-in DSA key pair generator supplied by the "SUN" provider):
X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encKey);Now you need a
KeyFactory
object to do the conversion. It needs to be one that works with DSA keys:KeyFactory keyFactory = KeyFactory.getInstance("DSA", "SUN");Finally, you can use the
KeyFactory
to generate aPublicKey
from the key specification:PublicKey pubKey = keyFactory.generatePublic(pubKeySpec);
Generating and Verifying Signatures |