Diffie-Hellman Key Exchange (DH)源代码
see also:http://www.example-code.com/vcpp/dh_key_exchange.asp#include <CkDh.h>#include <CkCrypt2.h>
void ChilkatSample(void)
{
//Create two separate instances of the DH object.
CkDh dhBob;
CkDh dhAlice;
bool success;
//Unlock the component once at program startup...
success = dhBob.UnlockComponent("Anything for 30-day trial");
if (success != true) {
printf("%s\n",dhBob.lastErrorText());
return;
}
//The DH algorithm begins with a large prime, P, and a generator, G.
//These don't have to be secret, and they may be transmitted over an insecure channel.
//The generator is a small integer and typically has the value 2 or 5.
//The Chilkat DH component provides the ability to use known
//"safe" primes, as well as a method to generate new safe primes.
//This example will use a known safe prime.Generating
//new safe primes is a time-consuming CPU intensive task
//and is normally done offline.
//Bob will choose to use the 2nd of our 8 pre-chosen safe primes.
//It is the Prime for the 2nd Oakley Group (RFC 2409) --
//1024-bit MODP Group.Generator is 2.
//The prime is: 2^1024 - 2^960 - 1 + 2^64 * { + 129093 }
dhBob.UseKnownPrime(2);
//The computed shared secret will be equal to the size of the prime (in bits).
//In this case the prime is 1024 bits, so the shared secret will be 128 bytes (128 * 8 = 1024).
//However, the result is returned as an SSH1-encoded bignum in hex string format.
//The SSH1-encoding prepends a 2-byte count, so the result is goingto be 2 bytes
//longer: 130 bytes.This results in a hex string that is 260 characters long (two chars
//per byte for the hex encoding).
const char * p;
long g;
//Bob will now send P and G to Alice.
p = dhBob.p();
g = dhBob.get_G();
//Alice calls SetPG to set P and G.SetPG checks
//the values to make sure it's a safe prime and will
//return false if not.
success = dhAlice.SetPG(p,g);
if (success != true) {
printf("P is not a safe prime\n");
return;
}
//Each side begins by generating an "E"
//value.The CreateE method has one argument: numBits.
//It should be set to twice the size of the number of bits
//in the session key.
//Let's say we want to generate a 128-bit session key
//for AES encryption.The shared secret generated by the Diffie-Hellman
//algorithm will be longer, so we'll hash the result to arrive at the
//desired session key length.However, the length of the session
//key we'll utlimately produce determines the value that should be
//passed to the CreateE method.
//In this case, we'll be creating a 128-bit session key, so pass 256 to CreateE.
//This setting is for security purposes only -- the value
//passed to CreateE does not change the length of the shared secret
//that is produced by Diffie-Hellman.
//Also, there is no need to pass in a value larger
//than 2 times the expected session key length.It suffices to
//pass exactly 2 times the session key length.
//Bob generates a random E (which has the mathematical
//properties required for DH).
const char * eBob;
eBob = dhBob.createE(256);
//Alice does the same:
const char * eAlice;
eAlice = dhAlice.createE(256);
//The "E" values are sent over the insecure channel.
//Bob sends his "E" to Alice, and Alice sends her "E" to Bob.
//Each side computes the shared secret by calling FindK.
//"K" is the shared-secret.
const char * kBob;
const char * kAlice;
//Bob computes the shared secret from Alice's "E":
kBob = dhBob.findK(eAlice);
//Alice computes the shared secret from Bob's "E":
kAlice = dhAlice.findK(eBob);
//Amazingly, kBob and kAlice are identical and the expected
//length (260 characters).The strings contain the hex encoded bytes of
//our shared secret:
printf("Bob's shared secret:\n");
printf("%s\n",kBob);
printf("Alice's shared secret (should be equal to Bob's)\n");
printf("%s\n",kAlice);
//To arrive at a 128-bit session key for AES encryption, Bob and Alice should
//both transform the raw shared secret using a hash algorithm that produces
//the size of session key desired. MD5 produces a 16-byte (128-bit) result, so
//this is a good choice for 128-bit AES.
//Here's how you would use Chilkat Crypt (a separate Chilkat component) to
//produce the session key:
CkCrypt2 crypt;
success = crypt.UnlockComponent("Anything for 30-day trial.");
if (success != true) {
printf("%s\n",crypt.lastErrorText());
return;
}
crypt.put_EncodingMode("hex");
crypt.put_HashAlgorithm("md5");
const char * sessionKey;
sessionKey = crypt.hashStringENC(kBob);
printf("128-bit Session Key:\n");
printf("%s\n",sessionKey);
//Encrypt something...
crypt.put_CryptAlgorithm("aes");
crypt.put_KeyLength(128);
crypt.put_CipherMode("cbc");
//Use an IV that is the MD5 hash of the session key...
const char * iv;
iv = crypt.hashStringENC(sessionKey);
//AES uses a 16-byte IV:
printf("Initialization Vector:\n");
printf("%s\n",iv);
crypt.SetEncodedKey(sessionKey,"hex");
crypt.SetEncodedIV(iv,"hex");
//Encrypt some text:
const char * cipherText64;
crypt.put_EncodingMode("base64");
cipherText64 = crypt.encryptStringENC("The quick brown fox jumps over the lazy dog");
printf("%s\n",cipherText64);
const char * plainText;
plainText = crypt.decryptStringENC(cipherText64);
printf("%s\n",plainText);
}
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