B&B Electronics Parallel Printer Card PIOC Manuel d'utilisateur télécharger pdf (Page 51)

GHI Electronics,LLC USBwiz User Manual

USBwiz Command Set

CK - Check Key

Checking the stored key:

1. The user application will generate a random 8 bytes and then encrypt them

using XTEA algorithm against the "secret key" that was used above

2. The user application will keep the original values and will send the new encrypted

values to USBwiz to the Check Key command"CK xxxxxxxxxxxxxxxx"

3. USBwiz will decrypt the incoming data using the "secret key” and send it back to

the application.

4. The returned value will match what the user started with only if the "secret key"

was correct.

Format CK<SP>8EncryptedBytes<CR>

!00<CR>

8CorrectBytes, if the stored

key was correct<CR>

!00<CR>

8Bytes The 8 encrypted bytes.

Example CK<SP>be5147f1cce6e72b<CR>

!00<CR>

0102030405060708<CR>

!00<CR>

be5147f1cce6e72b 8Bytes were

decrypted against the previous key

0102030405060708 The actual

bytes before decryption

XTEA Algorithm Code:

This is the Encryption algorithm:

v: an array of 8 bytes to encrypt

k: the "Secret key"

void Encrypt8ByteBlock(int32* v, int32* k) {

int32 v0=v[0], v1=v[1], i;

int32 sum=0, delta=0x9E3779B9;

for(i=0; i<32; i++) {

v0 += (v1 << 4 ^ v1 >> 5) + v1 ^ sum + k[sum & 3];

sum += delta;

v1 += (v0 << 4 ^ v0 >> 5) + v0 ^ sum + k[sum>>11 & 3];

}

v[0]=v0; v[1]=v1;

}

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B&B Electronics Parallel Printer Card PIOC Manuel d'utilisateur Page 51