Differences
This shows you the differences between two versions of the page.
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ic:laboratoare:09 [2019/11/09 20:19] dan.dragan |
ic:laboratoare:09 [2020/11/05 17:54] (current) acosmin.maria |
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| Line 10: | Line 10: | ||
| For this exercise, use OpenSSL commands to: | For this exercise, use OpenSSL commands to: | ||
| - | - generate a 16 byte random key | + | - generate a 16 byte random key; |
| - | - use the key to compute the SHA-1 HMAC of the page downloaded in the previous exercise | + | - use the key to compute the SHA-1 HMAC of the following message: "Laborator IC"; |
| + | - use the same key to compute the SHA-1 HMAC of the following message: "Laborator IC!". Notice the difference between the messages - a single character (e.g "!"). Observe that the message authentication codes are completely different. | ||
| Line 48: | Line 49: | ||
| </note> | </note> | ||
| - | <hidden>The solution is {{:ic:laboratoare:lab9_sol.zip|here}}.</hidden> | ||
| - | Before you start solving the exercises below, download the {{:ic:laboratoare:ic_lab10.zip|lab archive from here}}. | ||
| + | ==== Exercise 3 ==== | ||
| - | ==== Exercise 1 ==== | + | Before you start solving the exercises below, download the {{:ic:laboratoare:aesgcm.zip|lab archive from here}}. |
| - | The archive contains the source code for Exercise 2, but sadly it is encrypted. Luckily, we forgot to remove the password file from the archive. | + | The archive contains the source code for Exercise 4, but sadly it is encrypted. Luckily, we forgot to remove the password file from the archive. |
| Use ''openssl'' commands to decrypt the source file. | Use ''openssl'' commands to decrypt the source file. | ||
| Line 63: | Line 63: | ||
| </note> | </note> | ||
| + | ==== Exercise 4 ==== | ||
| - | ==== Exercise 2 ==== | + | <hidden> |
| + | |||
| + | <note hint> | ||
| + | The problem has been fixed, so no more code for students! | ||
| + | </note> | ||
| + | |||
| + | In case you didn't manage to solve Exercise 3 (more recent versions of openssl are not compatible with respect to the encryption/decryption using password), here is the lab starting code: | ||
| + | |||
| + | <code> | ||
| + | |||
| + | #include <openssl/evp.h> | ||
| + | #include <openssl/err.h> | ||
| + | #include <stdlib.h> | ||
| + | #include <stdint.h> | ||
| + | #include <stdio.h> | ||
| + | #include <string.h> | ||
| + | |||
| + | void hexdump(unsigned char * string, int length) { | ||
| + | int i; | ||
| + | for (i = 0; i < length; i++) { | ||
| + | printf("%02x", string[i]); | ||
| + | } | ||
| + | } | ||
| + | |||
| + | |||
| + | int aes_gcm_encrypt(unsigned char * ptext, | ||
| + | int plen, | ||
| + | unsigned char * key, | ||
| + | unsigned char * iv, | ||
| + | unsigned char ** ctext, | ||
| + | int * clen) { | ||
| + | |||
| + | EVP_CIPHER_CTX * ctx; | ||
| + | |||
| + | /* TODO Create new EVP Context */ | ||
| + | |||
| + | /* TODO Initialize context using 256-bit AES-GCM, Encryption operation */ | ||
| + | /* TODO Initialize Key and IV for the new context */ | ||
| + | |||
| + | /* TODO Encrypt data */ | ||
| + | |||
| + | /* TODO Finalize encryption context (computes and appends auth tag) */ | ||
| + | |||
| + | /* TODO Print tag */ | ||
| + | |||
| + | /* TODO Destroy context */ | ||
| + | |||
| + | return 0; | ||
| + | } | ||
| + | |||
| + | int aes_gcm_decrypt(unsigned char * ctext, | ||
| + | int clen, | ||
| + | unsigned char * key, | ||
| + | unsigned char * iv, | ||
| + | unsigned char ** ptext, | ||
| + | int * plen) { | ||
| + | |||
| + | EVP_CIPHER_CTX * ctx; | ||
| + | |||
| + | /* TODO Create new EVP Context */ | ||
| + | |||
| + | /* TODO Initialize context using 256-bit AES-GCM, Decryption operation */ | ||
| + | /* TODO Initialize Key and IV for the new context */ | ||
| + | |||
| + | /* TODO Submit tag data */ | ||
| + | |||
| + | /* TODO Decrypt data */ | ||
| + | |||
| + | /* TODO Finalize decryption context (verifies auth tag) */ | ||
| + | |||
| + | /* TODO Destroy context */ | ||
| + | |||
| + | return 0; | ||
| + | } | ||
| + | |||
| + | int main(int argc, char * argv[]) { | ||
| + | ERR_load_crypto_strings(); | ||
| + | |||
| + | unsigned char key[] = "0123456789abcdef0123456789abcdef"; /* 256-bit key */ | ||
| + | unsigned char iv[] = "0123456789ab"; /* 96-bit IV */ | ||
| + | |||
| + | unsigned char * ptext = (unsigned char *)"Hello, SSLWorld!\n"; | ||
| + | int plen = strlen((const char *)ptext); | ||
| + | |||
| + | unsigned char * ctext; | ||
| + | int clen; | ||
| + | |||
| + | printf("Plaintext = %s\n", ptext); | ||
| + | printf("Plaintext (hex) = "); hexdump(ptext, plen); printf("\n"); | ||
| + | |||
| + | aes_gcm_encrypt(ptext, plen, key, iv, &ctext, &clen); | ||
| + | printf("Ciphertext (hex) = "); hexdump(ctext, clen - 16); printf("\n"); | ||
| + | |||
| + | unsigned char * ptext2; | ||
| + | int plen2; | ||
| + | aes_gcm_decrypt(ctext, clen, key, iv, &ptext2, &plen2); | ||
| + | printf("Done decrypting!\n"); | ||
| + | |||
| + | ptext2[plen2] = '\0'; | ||
| + | printf("Plaintext = %s\n", ptext2); | ||
| + | |||
| + | if (memcmp(ptext, ptext2, strlen((const char *)ptext)) == 0) { | ||
| + | printf("Ok!\n"); | ||
| + | } else { | ||
| + | printf("Not ok :(\n"); | ||
| + | } | ||
| + | |||
| + | return 0; | ||
| + | } | ||
| + | </code> | ||
| + | |||
| + | </hidden> | ||
| In this exercise we'll use OpenSSL to encrypt and decrypt with AES-128-GCM. Unfortunately, AES-GCM is not supported by the command line utilities of OpenSSL so we'll have to implement it ourselves. | In this exercise we'll use OpenSSL to encrypt and decrypt with AES-128-GCM. Unfortunately, AES-GCM is not supported by the command line utilities of OpenSSL so we'll have to implement it ourselves. | ||
| Line 124: | Line 236: | ||
| See the open ssl manual [[https://www.openssl.org/docs/man1.1.0/crypto/EVP_aes_256_gcm.html|here]] page for EVP encrypt to see the usage of the EVP functions and an example similar to the one above. | See the open ssl manual [[https://www.openssl.org/docs/man1.1.0/crypto/EVP_aes_256_gcm.html|here]] page for EVP encrypt to see the usage of the EVP functions and an example similar to the one above. | ||
| </note> | </note> | ||
| - | |||
| - | <hidden> | ||
| - | The solution is {{:ic:laboratoare:lab10_sol.zip|here}}. | ||
| - | |||
| - | Alternative solution: [[https://paste.ubuntu.com/p/4XZpMtt9ZZ/|Source code]] | ||
| - | </hidden> | ||
