Add a sodium_bin2hex utility function.

README.markdown

@@ -135,11 +135,17 @@ Warning: if a region has been allocated on the heap, you still have
 to make sure that it can't get swapped to disk, possibly using
 `mlock(2)`.
 
-In order to compare memory zones in constant time, Sodium proides:
+In order to compare memory zones in constant time, Sodium provides:
 
     int      sodium_memcmp(const void * const b1_, const void * const b2_,
                            size_t size);
 
+And a convenience function for converting a binary buffer to a
+hexadecimal string:
+
+    char *   sodium_bin2hex(char * const hex, const size_t hexlen,
+                            const unsigned char *bin, const size_t binlen);
+
 ## New operations
 
 ### crypto_shorthash

src/libsodium/include/sodium/utils.h

@@ -25,6 +25,10 @@ void sodium_memzero(void * const pnt, const size_t len);
 SODIUM_EXPORT
 int sodium_memcmp(const void * const b1_, const void * const b2_, size_t size);
 
+SODIUM_EXPORT
+char *sodium_bin2hex(char * const hex, const size_t hexlen,
+                     const unsigned char *bin, const size_t binlen);
+
 #ifdef __cplusplus
 }
 #endif

src/libsodium/sodium/utils.c

@@ -63,3 +63,24 @@ _sodium_alignedcalloc(unsigned char ** const unaligned_p, const size_t len)
 
     return aligned;
 }
+
+char *
+sodium_bin2hex(char * const hex, const size_t hexlen,
+               const unsigned char *bin, const size_t binlen)
+{
+    static const char hexdigits[16] = "0123456789abcdef";
+    size_t            i = (size_t) 0U;
+    size_t            j = (size_t) 0U;
+
+    if (binlen >= SIZE_MAX / 2 || hexlen < binlen * 2U) {
+        abort();
+    }
+    while (i < binlen) {
+        hex[j++] = hexdigits[bin[i] >> 4];
+        hex[j++] = hexdigits[bin[i] & 0xf];
+        i++;
+    }
+    hex[j] = 0;
+
+    return hex;
+}

test/default/sodium_utils.c

@@ -8,17 +8,20 @@ int main(void)
 {
   unsigned char buf1[1000];
   unsigned char buf2[1000];
+  char          buf3[33];
 
   randombytes(buf1, sizeof buf1);
   memcpy(buf2, buf1, sizeof buf2);
-  printf ("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
+  printf("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
   sodium_memzero(buf1, 0U);
-  printf ("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
+  printf("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
   sodium_memzero(buf1, sizeof buf1 / 2);
-  printf ("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
-  printf ("%d\n", sodium_memcmp(buf1, buf2, 0U));
+  printf("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
+  printf("%d\n", sodium_memcmp(buf1, buf2, 0U));
   sodium_memzero(buf2, sizeof buf2 / 2);
-  printf ("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
-
+  printf("%d\n", sodium_memcmp(buf1, buf2, sizeof buf1));
+  printf("%s\n", sodium_bin2hex(buf3, 33U,
+                                (const unsigned char *)
+                                "0123456789ABCDEF", 16U));
   return 0;
 }

test/default/sodium_utils.exp

@@ -3,3 +3,4 @@
 255
 0
 0
+30313233343536373839414243444546