CTFs and solutions

openssl-dgst/HMAC_computation_EVP.c

@@ -0,0 +1,79 @@
+#include <stdio.h>
+#include <openssl/evp.h>
+#include <openssl/hmac.h>
+#include <openssl/err.h>
+#include <string.h>
+
+#define MAXBUF 1024
+
+void handle_errors(){
+    ERR_print_errors_fp(stderr);
+    abort();
+}
+
+
+int main(int argc, char **argv){
+       
+       
+        unsigned char key[] = "deadbeefdeadbeef";
+        unsigned char secret[] = "this_is_my_secret";
+        if(argc != 2){
+            fprintf(stderr,"Invalid parameters. Usage: %s filename\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");
+                exit(1);
+        }
+
+
+
+       //EVP_MD_CTX *EVP_MD_CTX_new(void);
+       //pedantic mode? Check if md == NULL
+		EVP_MD_CTX  *hmac_ctx = EVP_MD_CTX_new();
+
+        //int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
+        // int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
+        // Returns 1 for success and 0 for failure.
+        EVP_PKEY *hkey;
+        hkey = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, NULL, key, 16);
+        
+        if(!EVP_DigestSignInit(hmac_ctx, NULL, EVP_sha512(), NULL, hkey))
+            handle_errors();
+
+        size_t n;
+        unsigned char buffer[MAXBUF];
+        if(!EVP_DigestSignUpdate(hmac_ctx, secret, strlen(secret)))
+            handle_errors();
+        while((n = fread(buffer,1,MAXBUF,f_in)) > 0){
+        // Returns 1 for success and 0 for failure.
+            if(!EVP_DigestSignUpdate(hmac_ctx, buffer, n))
+                handle_errors();
+        }
+        if(!EVP_DigestSignUpdate(hmac_ctx, secret, strlen(secret)))
+            handle_errors();
+
+        unsigned char hmac_value[EVP_MD_size(EVP_sha512())];
+        size_t hmac_len = EVP_MD_size(EVP_sha512
+            ());
+
+        //int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned size_t *s);
+        // EVP_DigestSignFinal(hmac_ctx, NULL, &hmac_len);
+        if(!EVP_DigestSignFinal(hmac_ctx, hmac_value, &hmac_len))
+            handle_errors();
+
+        // void EVP_MD_CTX_free(EVP_MD_CTX *ctx);
+		EVP_MD_CTX_free(hmac_ctx);
+
+        printf("CRYPTO25{");
+        for(int i = 0; i < hmac_len; i++)
+			     printf("%02x", hmac_value[i]);
+        printf("}");
+
+
+	return 0;
+
+}