(Extra 12) GD32L233 Review - CAU Encryption and Decryption (Tease the Editor)

韵湖葱白

(Extra 12) GD32L233 Review - CAU Encryption and Decryption (Tease the Editor) [Copy link]

<i class="pstatus"> This post was last edited by Yunhu Congbai on 2022-3-7 11:52 </i> ## Preface The experiments have been completed, but I have not had time to sort out the article. I almost forgot about it after a long time. This article tests CAU encryption. The encryption interface is relatively simple, but the principle behind it is relatively complicated. It is a roundabout mathematical formula, which I will not explain here. Take the electronic codebook mode ECB as an example. It is the oldest and simplest mode. The encrypted data is divided into several groups, and the size of each group is the same as the encryption key length; then each group is encrypted with the same key, such as the DES algorithm. If the length of the last group is less than 64 bits, it must be padded to 64 bits. Definition: ``` Enc(X,Y) is the encryption function Dec(X,Y) is the decryption function Key is the encryption key; Pi (i = 0,1…n) is the plaintext block, size is 64bit; Ci (i = 0,1…n) is the ciphertext block, size is 64bit; ``` ECB encryption algorithm can be expressed as: ``` Ci = Enc(Key, Pi) ``` ECB decryption algorithm can be expressed as: ``` Pi = Dec(Key,Ci) ``` Characteristics of ECB algorithm: - The length of Key, plaintext and ciphertext must be 64 bits each time; - Duplicate ordering of data blocks does not need to be detected; - The same plaintext block (using the same key) produces the same ciphertext block, which is vulnerable to dictionary attacks; - An error only affects one ciphertext block; ## Example, for example, to encrypt a URL: https://en.eeworld.com/bbs/thread-1191754-1-1.html The calling interface is very simple, which is `cau_des_ecb`, and the filling is `zero padding`. Code: ``` static void cau_test(void) { #ifdef CAU_TEST __attribute__((aligned(4))) uint8_t message[64] = "https://en.eeworld.com/bbs/thread-1191754-1-1.html"; __attribute__((aligned(4))) uint8_t key[8] = "12345678"; __attribute__( (aligned(4))) uint8_t encrypt_result[65] = {'\0'}; cau_parameter_struct text; rcu_periph_clock_enable(RCU_CAU); cau_deinit(); cau_struct_para_init(&text); /* encryption in DES ECB mode */ text.alg_dir = CAU_ENCRYPT; text.key = key; text.input = message; in_length = 64; if (SUCCESS == cau_des_ecb(&text, encrypt_result)) { printf("%s\r\n", encrypt_result); } #endif } ``` Tested on https://oktools.net/des, we get: Ciphertext (HEX): 49d7997faa52e7f787f8a086c93603ecf17657b2fca877be973940021ef79967eb690d428e998db0888788c9cbe0842c560fcfdf012d0edc Ciphertext (BASE64): SdeZf6pS5/eH+KCGyTYD7PF2V7L8qHe+lzlAAh73mWfraQ1CjpmNsIiHiMnL4IQsVg/P3wEtDtw= Our test results:  When the contents we encrypt are very similar, their ciphertexts are also very similar: For example: https://en.eeworld.com/bbs/thread-1193072-1-1.html The ciphertext is: 49d7997faa52e7f787f8a086c93603ecf17657b2fca877be973940021ef79967eeccfeb9a8373972888788c9cbe0842c560fcfdf012d0edc, which is very similar to the previous test. Test a different one: For example: https://mp.weixin.qq.com/s/ZWl1Q8bLrAr-qKYhV4w4BA The ciphertext is: 4a0abde163ab83f2750b82fd3e9cdf84cdf44866b991bbb5134c1178ba90c9115eb1f2f30047e67e7b9d69bde70b75d5965d73eaaece4d74 Ciphertext (BASE64): Sgq94WOrg/J1C4L9PpzfhM30SGa5kbu1E0wReLqQyRFesfLzAEfmfnudab3nC3XVll1z6q7OTXQ= The difference from the previous one is huge. ## Just to tease the editor, here is a secret Chinese text, which has been encrypted. Let's see if the editor knows what to do? The original text is as follows (only contains some keywords): `******大陆******赤日******斗******守******` The ciphertext is as follows: HEX:Base64: JAUrabNvIjFsKIDQo6F8iWU5ftSBw4MCayFgeOEnAwi+C/chRzFdbvtH/N30Zz7NPPzUkQBEW0aEyhh4trIVSZyfQS6yLLgHSiOwvFYXROe07llzBXpDhZNcbCaqhtbL1N5x0BSYwJg1 75+zfmHvCiPA4qHlT3ltKuO4xjTXnP2Gf3yLBIDnwuTHN2D2Squ6LI6YPBZO7oxBYK2iTjZIGMXDBM7gjbkm8Ro2LVd35fJQEFkkhdUYu90lGPp1 6y+yyUxe6nRGltIjSRVSH4LAm9gkqFffAniK1+fcRwhox7Kv6y4EQOxBH/YWq6/jPjXqKg2ekwh6iTRwujVVurmYDU0LNIegBIK6F+UJ3NRdgFSph8dLCFHoab6Bo19X45EsYm+QIawhmJrjf0Qs nExnMnvwObd8gbZz0ujspa6D9ERd8OkDsLS5juHrr93b+xe6L///XYSFL1iwS7fcJXKuTYi0U0iSKMfhl3xrnB0q8brEiHbArLmosQ== Decryption tips: Chinese->Convert to unicode->DES ECB(key:12345678)  

Jacktang

How to play the last encryption

韵湖葱白

Jacktang posted on 2022-3-7 21:19 How to play the last encryption

Hahaha, I'm just kidding.

This is the encryption process: Chinese->convert to unicode->DES ECB (key:12345678)

Even the key is told, the decryption is the opposite.