CTFs and solutions

openssl-enc/COLORFGBG=15;0

@@ -0,0 +1,2 @@
+	<09><><1C><><11>Z<EFBFBD>
+<13><>5X<35><58>1<>s<EFBFBD><73>b7b<>\k<>HP&<15>p<EFBFBD><70>ܫ8

openssl-enc/code.c

@@ -0,0 +1,118 @@
+#include <stdio.h>
+#include <string.h>
+
+#include <openssl/evp.h>
+#include <openssl/err.h>
+
+
+#define ENCRYPT 1
+#define DECRYPT 0
+#define MAX_BUFFER 1024
+
+void handle_errors(){
+    ERR_print_errors_fp(stderr);
+    abort();
+}
+
+int main(int argc, char **argv)
+{
+
+//  int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, const unsigned char *key, const unsigned char *iv, int enc);
+//  int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl, const unsigned char *in, int inl);
+//  int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
+
+
+
+
+    if(argc != 5){
+        fprintf(stderr,"Invalid parameters. Usage: %s file_in key iv file_out\n",argv[0]);
+        exit(1);
+    }
+
+    FILE *f_in;
+    if((f_in = fopen(argv[1],"r")) == NULL) {
+            fprintf(stderr,"Couldn't open the input file, try again\n");
+            abort();
+    }
+ 
+    if(strlen(argv[2])!=64){
+        fprintf(stderr,"Wrong key length\n");
+        abort();
+    }   
+    if(strlen(argv[3])!=32){
+        fprintf(stderr,"Wrong IV length\n");
+        abort();
+    }
+    
+    FILE *f_out;
+    if((f_out = fopen(argv[4],"wb")) == NULL) {
+            fprintf(stderr,"Couldn't open the output file, try again\n");
+            abort();
+    }
+
+    unsigned char key[strlen(argv[2])/2];
+    for(int i = 0; i < strlen(argv[2])/2;i++){
+        sscanf(&argv[2][2*i],"%2hhx", &key[i]);
+    }
+
+    unsigned char iv[strlen(argv[3])/2];
+    for(int i = 0; i < strlen(argv[3])/2;i++){
+        sscanf(&argv[3][2*i],"%2hhx", &iv[i]);
+    }
+
+    /* Load the human readable error strings for libcrypto */
+    ERR_load_crypto_strings();
+    /* Load all digest and cipher algorithms */
+    OpenSSL_add_all_algorithms();
+
+
+
+    // pedantic mode: check NULL
+    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+
+    if(!EVP_CipherInit(ctx,EVP_chacha20(), key, iv, DECRYPT))
+        handle_errors();
+
+    int length;
+    unsigned char ciphertext[MAX_BUFFER+16];
+
+    int n_read;
+    unsigned char buffer[MAX_BUFFER];
+
+    while((n_read = fread(buffer,1,MAX_BUFFER,f_in)) > 0){
+        printf("n_Read=%d-",n_read);
+        if(!EVP_CipherUpdate(ctx,ciphertext,&length,buffer,n_read))
+            handle_errors();
+        printf("length=%d\n",length);
+        if(fwrite(ciphertext, 1, length,f_out) < length){
+            fprintf(stderr,"Error writing the output file\n");
+            abort();
+        }
+    }
+            
+    if(!EVP_CipherFinal_ex(ctx,ciphertext,&length))
+        handle_errors();
+
+    printf("lenght=%d\n",length);
+
+    if(fwrite(ciphertext,1, length, f_out) < length){
+        fprintf(stderr,"Error writing in the output file\n");
+        abort();
+    }
+
+    EVP_CIPHER_CTX_free(ctx);
+
+    fclose(f_in);
+    fclose(f_out);
+
+    printf("File encrypted!\n");
+
+
+    // completely free all the cipher data
+    CRYPTO_cleanup_all_ex_data();
+    /* Remove error strings */
+    ERR_free_strings();
+
+    return 0;
+}
+

openssl-enc/enc1.c

@@ -0,0 +1,44 @@
+#include <stdio.h>
+#include <string.h>
+
+#include <openssl/evp.h>
+
+
+#define ENCRYPT 1
+#define DECRYPT 0
+
+int main()
+{
+    
+
+    unsigned char key[] = "0123456789ABCDEF";
+    unsigned char iv[]  = "1111111111111111";
+
+    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+    EVP_CipherInit(ctx,EVP_aes_128_cbc(), key, iv, ENCRYPT);
+    //This disable the padding
+    EVP_CIPHER_CTX_set_padding(ctx, 0);
+
+    unsigned char plaintext[] = "This is the plaintext to encrypt."; //len 33
+    unsigned char ciphertext[48];
+
+    int update_len, final_len;
+    int ciphertext_len=0;
+
+    EVP_CipherUpdate(ctx,ciphertext,&update_len,plaintext,strlen(plaintext));
+    ciphertext_len+=update_len;
+    printf("update size: %d\n",ciphertext_len);
+
+    EVP_CipherFinal_ex(ctx,ciphertext+ciphertext_len,&final_len);
+    ciphertext_len+=final_len;
+
+    EVP_CIPHER_CTX_free(ctx);
+
+    printf("Ciphertext lenght = %d\n", ciphertext_len);
+    for(int i = 0; i < ciphertext_len; i++)
+        printf("%02x", ciphertext[i]);
+    printf("\n");
+
+    return 0;
+}
+

openssl-enc/file.enc

@@ -0,0 +1 @@
+<EFBFBD>$<24>4<EFBFBD>jz|<7C>Z<EFBFBD><5A><EFBFBD>9<12><><EFBFBD><EFBFBD><EFBFBD>mi2+`<60>

openssl-enc/file.txt

@@ -0,0 +1 @@
+CRYPTO25{MyDecryptedString}

openssl-enc/guess.py

@@ -0,0 +1,50 @@
+import os
+cipher_names = [
+    "AES-128-CBC",
+    "AES-192-CBC",
+    "AES-256-CBC",
+    "AES-128-CTR",
+    "AES-192-CTR",
+    "AES-256-CTR",
+    "AES-128-GCM",
+    "AES-192-GCM",
+    "AES-256-GCM",
+    "DES-CBC",
+    "DES-EDE3-CBC",
+    "ChaCha20-Poly1305",
+    "Camellia-128-CBC",
+    "Camellia-192-CBC",
+    "Camellia-256-CBC",
+    "Camellia-128-CTR",
+    "Camellia-192-CTR",
+    "Camellia-256-CTR",
+    "BF-CBC", # Blowfish
+    "BF-CFB", # Blowfish
+    "BF-OFB", # Blowfish
+    "BF-ECB", # Blowfish
+    "CAST5-CBC", # CAST5
+    "CAST5-CFB", # CAST5
+    "CAST5-OFB", # CAST5
+    "CAST5-ECB", # CAST5
+    "IDEA-CBC", # IDEA
+    "IDEA-CFB", # IDEA
+    "IDEA-OFB", # IDEA
+    "IDEA-ECB", # IDEA
+    "RC2-CBC", # RC2
+    "RC2-CFB", # RC2
+    "RC2-OFB", # RC2
+    "RC2-ECB", # RC2
+    "RC4", # RC4 (stream cipher)
+    "ARIA-128-CBC", #ARIA
+    "ARIA-192-CBC", #ARIA
+    "ARIA-256-CBC", #ARIA
+    "ARIA-128-CTR", #ARIA
+    "ARIA-192-CTR", #ARIA
+    "ARIA-256-CTR", #ARIA
+    "ARIA-128-GCM", #ARIA
+    "ARIA-192-GCM", #ARIA
+    "ARIA-256-GCM", #ARIA
+]
+
+for i in cipher_names:
+    os.system("./guess.exe guessalgo.enc "+i)

openssl-enc/guessalgo.c

@@ -0,0 +1,121 @@
+#include <stdio.h>
+#include <string.h>
+
+#include <openssl/evp.h>
+#include <openssl/err.h>
+
+
+#define ENCRYPT 1
+#define DECRYPT 0
+#define MAX_BUFFER 1024
+
+void handle_errors(){
+    ERR_print_errors_fp(stderr);
+    abort();
+}
+
+int main(int argc, char **argv)
+{
+
+//  int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, const unsigned char *key, const unsigned char *iv, int enc);
+//  int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl, const unsigned char *in, int inl);
+//  int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
+
+
+
+
+    if(argc != 3){
+        fprintf(stderr,"Invalid parameters. Usage: %s file_in ALGO-TO-USE\n",argv[0]);
+        exit(1);
+    }
+
+
+    FILE *f_in;
+    if((f_in = fopen(argv[1],"r")) == NULL) {
+            fprintf(stderr,"Couldn't open the input file, try again\n");
+            abort();
+    }
+    /*
+    if(strlen(argv[2])!=32){
+        fprintf(stderr,"Wrong key length\n");
+        abort();
+    }   
+    if(strlen(argv[3])!=32){
+        fprintf(stderr,"Wrong IV length\n");
+        abort();
+    }
+    */
+    /*FILE *f_out;
+    if((f_out = fopen(argv[2],"wb")) == NULL) {
+            fprintf(stderr,"Couldn't open the output file, try again\n");
+            abort();
+    }*/
+    unsigned char key[] = "0123456789ABCDEF";
+    unsigned char iv[] = "0123456789ABCDEF";
+    /*unsigned char key[strlen(argv[2])/2];
+    for(int i = 0; i < strlen(argv[2])/2;i++){
+        sscanf(&argv[2][2*i],"%2hhx", &key[i]);
+    }
+
+    unsigned char iv[strlen(argv[3])/2];
+    for(int i = 0; i < strlen(argv[3])/2;i++){
+        sscanf(&argv[3][2*i],"%2hhx", &iv[i]);
+    }
+    */
+    /* Load the human readable error strings for libcrypto */
+    ERR_load_crypto_strings();
+    /* Load all digest and cipher algorithms */
+    OpenSSL_add_all_algorithms(); // deprecated since version 1.1.1
+
+
+
+    // pedantic mode: check NULL
+    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+
+    if(!EVP_CipherInit(ctx,EVP_get_cipherbyname(argv[2]), key, iv, DECRYPT))
+        handle_errors();
+    EVP_CIPHER_CTX_set_padding(ctx,0);
+    int length;
+    unsigned char ciphertext[MAX_BUFFER+16];
+
+    int n_read;
+    unsigned char buffer[MAX_BUFFER];
+
+    while((n_read = fread(buffer,1,MAX_BUFFER,f_in)) > 0){
+        //printf("n_Read=%d-",n_read);
+        if(!EVP_CipherUpdate(ctx,ciphertext,&length,buffer,n_read))
+            handle_errors();
+        //printf("length=%d\n",length);
+
+        /*if(fwrite(ciphertext, 1, length,f_out) < length){
+            fprintf(stderr,"Error writing the output file\n");
+            abort();
+        }*/
+    }
+            
+    if(!EVP_CipherFinal_ex(ctx,ciphertext,&length))
+        handle_errors();
+
+    //printf("lenght=%d\n",length);
+    printf("ALGORITHM:%s, Output: %s\n", argv[2], ciphertext);
+    /*if(fwrite(ciphertext,1, length, f_out) < length){
+        fprintf(stderr,"Error writing in the output file\n");
+        abort();
+    }
+    */
+    EVP_CIPHER_CTX_free(ctx);
+
+    fclose(f_in);
+//    fclose(f_out);
+
+    //printf("File decrypted!\n");
+
+
+    // completely free all the cipher data
+    CRYPTO_cleanup_all_ex_data();
+    /* Remove error strings */
+    ERR_free_strings();
+
+    return 0;
+}
+

openssl-enc/guessalgo.enc

@@ -0,0 +1 @@
+e<EFBFBD>~<04>Mv<4D><76><EFBFBD>6<EFBFBD><36><EFBFBD>9"<22>h<EFBFBD><68>|<7C>/y0o<03>Q><3E>