Java Public/Private Key Algorithm

Today, I saw a Java Public/Private Key algorithm on the Internet. Very good...

Add the information public final byte [] Sign () throws signatureexception to return the signature array, provided that initsign and updatepublic final void initverify (publickey) throws invalidkeyexception uses the specified public key initialization parameter: Public final Boolean verify (byte [] signature) When publickey is used for verification throws signatureexception to verify whether the signature is valid, provided that the parameter has been initverify initialized: signature signature array */import Java. security. *; import Java. security. spec. *; public class testdsa {public static void main (string [] ARGs) throws Java. security. nosuchalgorithmexception, Java. lang. exception {testdsa my = new testdsa (); my. run ();} public void run () {// digital signature to generate a key pair // The first step is to generate a key pair. If the key pair has been generated, skip this process, myprikey. dat needs to be saved locally // while mypubkey. dat to publish to other users if (New Java. io. file ("myprikey. dat ")). exists () = false) {If (generatekey () = false) {system. out. println ("failed to generate key pair"); Return ;}/// step 2, this user // reads the private key from the file, sign a string and save it in a file (myinfo. in dat) // and then put myinfo. dat is sent out // For convenience, the digital signature is also put in myifno. in the DAT file, you can also send try {Java. io. objectinputstream in = new Java. io. objectinputstream (New Java. io. fileinputstream ("myprikey. dat "); privatekey myprikey = (privatekey) in. readobject (); In. close (); // Java. security. spec. x509encodedkeyspec pubx509 = new Java. security. spec. x509encodedkeyspec (bx509); // Java. security. spec. x509encodedkeyspec pubkeyencode = Java. security. spec. x509encodedkeyspec string myinfo = "this is my information"; // The information to be signed // generate a digital signature using the private key pair information Java. security. signature signet = Java. security. signature. getinstance ("DSA"); signet. initsign (myprikey); signet. update (myinfo. getbytes (); byte [] signed = signet. sign (); // digital signature of information system. out. println ("signed (Signature content) =" + byte2hex (Signed); // Save the information and digital signature in a file. java. io. objectoutputstream out = new Java. io. objectoutputstream (New Java. io. fileoutputstream ("myinfo. dat "); out. writeobject (myinfo); out. writeobject (Signed); out. close (); system. out. println ("signature and file generation succeeded");} catch (Java. lang. exception e) {e. printstacktrace (); system. out. println ("failed to sign and generate a file") ;}; // step 3 // others obtain the public key and file of the user in public mode. // others use the public key of the user, check the file. If the file is successfully checked, it indicates the information published by this user. // try {Java. io. objectinputstream in = new Java. io. objectinputstream (New Java. io. fileinputstream ("mypubkey. dat "); publickey pubkey = (publickey) in. readobject (); In. close (); system. out. println (pubkey. getformat (); In = new Java. io. objectinputstream (New Java. io. fileinputstream ("myinfo. dat "); string info = (string) in. readobject (); byte [] signed = (byte []) in. readobject (); In. close (); Java. security. signature signetcheck = Java. security. signature. getinstance ("DSA"); signetcheck. initverify (pubkey); signetcheck. update (info. getbytes (); If (signetcheck. verify (Signed) {system. out. println ("info =" + info); system. out. println ("normal signature");} else system. out. println ("non-signature normal");} catch (Java. lang. exception e) {e. printstacktrace () ;};}// generate a pair of file myprikey. dat and mypubkey. dat --- private key and public key. // the public key must be sent by the user (file, network, and other methods) to other users. The private key is stored in the local public Boolean generatekey () {try {Java. security. keypairgenerator keygen = Java. security. keypairgenerator. getinstance ("DSA"); // securerandom secrand = new securerandom (); // secrand. setseed ("tttt ". getbytes (); // initialize the random generator // keygen. initialize (576, secrand); // initialize the key generator keygen. initialize (512); keypair keys = keygen. genkeypair (); // keypair keys = keygen. generatekeypair (); // generate the key group publickey pubkey = keys. getpublic (); privatekey prikey = keys. getprivate (); Java. io. objectoutputstream out = new Java. io. objectoutputstream (New Java. io. fileoutputstream ("myprikey. dat "); out. writeobject (prikey); out. close (); system. out. println ("Write object prikeys OK"); out = new Java. io. objectoutputstream (New Java. io. fileoutputstream ("mypubkey. dat "); out. writeobject (pubkey); out. close (); system. out. println ("Write object pubkeys OK"); system. out. println ("key pair generated successfully"); Return true;} catch (Java. lang. exception e) {e. printstacktrace (); system. out. println ("failed to generate the key pair"); Return false ;};} Public String byte2hex (byte [] B) {string HS = ""; string stmp = ""; for (INT n = 0; n