Add get_encryption_params.

This function is used to split the links to encrypted content into
useful parts.

formats.c

@@ -6,7 +6,7 @@
 /*
  * Set print to true to print value, otherwise returns dynamic string with the number
  */
-char *print_hex(uint8_t *buf, int len, bool print)
+char *print_hex(const uint8_t *buf, int len, bool print)
 {
     char *rv = NULL;
 
@@ -36,6 +36,38 @@ char *print_hex(uint8_t *buf, int len, bool print)
     return rv;
 }
 
-// TODO:
-// buffer to base64
-// base64 to buffer
+static bool is_hex_char(char c)
+{
+    return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
+}
+
+// from https://lemire.me/blog/2019/04/17/parsing-short-hexadecimal-strings-efficiently/
+static uint32_t convert_hex_char(uint8_t c) {
+    return (c & 0xF) + 9 * (c >> 6);
+}
+
+static uint8_t assemble_u8(const char *cs)
+{
+    uint8_t rv = 0;
+    for (int i = 0; i < 2; i++) {
+        int index = !i;
+        rv |= convert_hex_char(cs[i]) << (4 * index);
+    }
+    return rv;
+}
+
+int decode_hex(const char *s, uint8_t *output, int len)
+{
+    for (int i = 0; i < len; i++) {
+        int j = i * 2;
+        int k = j + 1;
+
+        if (is_hex_char(s[j]) && is_hex_char(s[k])) {
+            output[i] = assemble_u8(s + j);
+        } else {
+            return -1;
+        }
+    }
+
+    return 0;
+}

purr.h

@@ -55,6 +55,7 @@ int socket_write(void *, const uint8_t *, size_t);
 
 /* urls.c */
 int clean_up_link(const char *, char *, char *, char *);
+int get_encryption_params(char *, uint8_t **, uint8_t **);
 int host_connect(const char *, const char *, bool);
 
 /* files.c */
@@ -68,7 +69,8 @@ size_t mmap_to_ssl(struct transmission_information);
 int send_and_receive(struct connection_information *);
 
 /* formats.c */
-char *print_hex(uint8_t *, int, bool);
+char *print_hex(const uint8_t *, int, bool);
+int decode_hex(const char *, uint8_t *, int);
 
 /* encrypt.c */
 struct mmap_file encrypt_mmap(struct mmap_file, uint8_t **, uint8_t **);

tests.c

@@ -20,6 +20,22 @@ static int compare_strings(const char *expected, const char *result, const char
     return rv;
 }
 
+static int compare_arrays(const uint8_t *expected, const uint8_t *result, size_t len, const char *function)
+{
+    int rv = 0;
+
+    printf("%s(): ", function);
+    if (memcmp(expected, result, len)) {
+        rv = 1;
+        puts("failure");
+        printf("expected: %s\ngot: %s\n", print_hex(expected, len, false), print_hex(result, len, false));
+    } else {
+        puts("success");
+    }
+
+    return rv;
+}
+
 int main()
 {
     int rv = 0;
@@ -48,6 +64,21 @@ int main()
         rv = compare_strings("/", path, "clean_up_link") ? 1 : rv;
         rv = compare_strings("80", port, "clean_up_link") ? 1 : rv;
         assert(portn == HTTP_PORT);
+
+        dirty = "https://bsd.ac/paste.html#sieqaqk_73fe_df51";
+        portn = clean_up_link(dirty, clean, path, port);
+        rv = compare_strings("bsd.ac", clean, "clean_up_link") ? 1 : rv;
+        rv = compare_strings("/paste.html#sieqaqk_73fe_df51", path, "clean_up_link") ? 1 : rv;
+        rv = compare_strings("443", port, "clean_up_link") ? 1 : rv;
+        assert(portn == HTTPS_PORT);
+        uint8_t key_exc[KEY_LEN] = {0x73, 0xfe};
+        uint8_t iv_exc[IV_LEN] = {0xdf, 0x51};
+        uint8_t *key, *iv;
+        int err = get_encryption_params(path, &key, &iv);
+        rv = compare_strings("/sieqaqk", path, "get_encryption_params") ? 1 : rv;
+        rv = compare_arrays(key_exc, key, KEY_LEN, "get_encryption_params") ? 1 : rv;
+        rv = compare_arrays(iv_exc, iv, IV_LEN, "get_encryption_params") ? 1 : rv;
+        assert(err == 0);
     }
 
     return rv;

urls.c

@@ -1,5 +1,6 @@
 #include <string.h>
 #include <unistd.h>
+#include <stdlib.h>
 
 #include <arpa/inet.h>
 #include <netdb.h>
@@ -55,6 +56,58 @@ int clean_up_link(const char *dirty, char *clean, char *path, char *port)
     return portn;
 }
 
+#define MALFORM_ERROR(p) do{if((p) == NULL || (p)[1] == 0) {fputs("get_encryption_params(): malformed URL\n", stderr); return rv;}}while(0);
+
+int get_encryption_params(char *path, uint8_t **keyp, uint8_t **ivp)
+{
+    int rv = -1;
+    // parse path in format: "/paste.html#<actual_path>_<key>[_<iv>]"
+    // will update path to point to the proper piece
+    uint8_t *key = calloc(KEY_LEN, 1);
+    uint8_t *iv = calloc(IV_LEN, 1);
+    char *path_temp = calloc(strlen(path), 1);
+    if (key == NULL || iv == NULL || path_temp == NULL) {
+        perror("calloc()");
+        return rv;
+    }
+    *keyp = key;
+    *ivp = iv;
+
+    char *hash = strchr(path, '#');
+    MALFORM_ERROR(hash);
+    char *underscore = strchr(hash + 1, '_');
+    MALFORM_ERROR(underscore);
+    underscore[0] = 0;
+
+    sprintf(path_temp, "/%s", hash + 1);
+
+    char *key_start = underscore + 1;
+    underscore = strchr(key_start, '_');
+    MALFORM_ERROR(underscore);
+    underscore[0] = 0;
+    char *iv_start = underscore + 1;
+
+    size_t key_s_len = strlen(key_start), iv_s_len = strlen(iv_start);
+    // odd number of chars is an error, as well as being too big
+    if (key_s_len & 1 || iv_s_len & 1 || key_s_len / 2 > KEY_LEN || iv_s_len / 2 > IV_LEN) {
+        fputs("get_encryption_params(): malformed KEY and/or IV input\n", stderr);
+        return rv;
+    }
+
+    int err = decode_hex(key_start, key, key_s_len / 2)
+        | decode_hex(iv_start, iv, iv_s_len / 2);
+    if (err) {
+        fputs("get_encryption_params(): malformed KEY and/or IV input\n", stderr);
+        return rv;
+    }
+
+    strcpy(path, path_temp);
+    free(path_temp);
+
+    rv = 0;
+    return rv;
+}
+
 int host_connect(const char *host, const char *port, bool debug)
 {
     struct addrinfo hints = { 0 }, *si = NULL;