avutil/random_seed: add av_random_bytes()

Uses the existing code for av_get_random_seed() to return a buffer with
cryptographically secure random data, or an error if none could be generated.

Signed-off-by: James Almer <jamrial@gmail.com>

1 files changed, 22 insertions, 11 deletions

diff --git a/libavutil/random_seed.c b/libavutil/random_seed.c
index a51149235b..f5c291263e 100644
--- a/libavutil/random_seed.c
+++ b/libavutil/random_seed.c
@@ -46,7 +46,7 @@
 #define TEST 0
 #endif
 
-static int read_random(uint32_t *dst, const char *file)
+static int read_random(uint8_t *dst, size_t len, const char *file)
 {
 #if HAVE_UNISTD_H
     FILE *fp = avpriv_fopen_utf8(file, "r");
@@ -54,10 +54,10 @@ static int read_random(uint32_t *dst, const char *file)
 
     if (!fp)
         return AVERROR_UNKNOWN;
-    err = fread(dst, 1, sizeof(*dst), fp);
+    err = fread(dst, 1, len, fp);
     fclose(fp);
 
-    if (err != sizeof(*dst))
+    if (err != len)
         return AVERROR_UNKNOWN;
 
     return 0;
@@ -121,27 +121,38 @@ static uint32_t get_generic_seed(void)
     return AV_RB32(digest) + AV_RB32(digest + 16);
 }
 
-uint32_t av_get_random_seed(void)
+int av_random_bytes(uint8_t* buf, size_t len)
 {
-    uint32_t seed;
+    int err;
 
 #if HAVE_BCRYPT
     BCRYPT_ALG_HANDLE algo_handle;
     NTSTATUS ret = BCryptOpenAlgorithmProvider(&algo_handle, BCRYPT_RNG_ALGORITHM,
                                                MS_PRIMITIVE_PROVIDER, 0);
     if (BCRYPT_SUCCESS(ret)) {
-        NTSTATUS ret = BCryptGenRandom(algo_handle, (UCHAR*)&seed, sizeof(seed), 0);
+        NTSTATUS ret = BCryptGenRandom(algo_handle, (PUCHAR)buf, len, 0);
         BCryptCloseAlgorithmProvider(algo_handle, 0);
         if (BCRYPT_SUCCESS(ret))
-            return seed;
+            return 0;
     }
 #endif
 
 #if HAVE_ARC4RANDOM
-    return arc4random();
+    arc4random_buf(buf, len);
+    return 0;
 #endif
 
-    if (!read_random(&seed, "/dev/urandom"))
-        return seed;
-    return get_generic_seed();
+    err = read_random(buf, len, "/dev/urandom");
+
+    return err;
+}
+
+uint32_t av_get_random_seed(void)
+{
+    uint32_t seed;
+
+    if (av_random_bytes((uint8_t *)&seed, sizeof(seed)) < 0)
+        return get_generic_seed();
+
+    return seed;
 }