1 files changed, 160 insertions, 0 deletions
diff --git a/libc-top-half/sources/arc4random.c b/libc-top-half/sources/arc4random.c
new file mode 100644
index 0000000..9898206
--- /dev/null
+++ b/libc-top-half/sources/arc4random.c
@@ -0,0 +1,160 @@
+#include <assert.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+#define RNG_RESERVE_LEN 512
+
+#define CHACHA20_KEYBYTES 32
+#define CHACHA20_BLOCKBYTES 64
+
+#define ROTL32(x, b) (uint32_t)(((x) << (b)) | ((x) >> (32 - (b))))
+
+#define CHACHA20_QUARTERROUND(A, B, C, D) \
+    A += B;                               \
+    D = ROTL32(D ^ A, 16);                \
+    C += D;                               \
+    B = ROTL32(B ^ C, 12);                \
+    A += B;                               \
+    D = ROTL32(D ^ A, 8);                 \
+    C += D;                               \
+    B = ROTL32(B ^ C, 7)
+
+static void CHACHA20_ROUNDS(uint32_t st[16])
+{
+    int i;
+
+    for (i = 0; i < 20; i += 2) {
+        CHACHA20_QUARTERROUND(st[0], st[4], st[8], st[12]);
+        CHACHA20_QUARTERROUND(st[1], st[5], st[9], st[13]);
+        CHACHA20_QUARTERROUND(st[2], st[6], st[10], st[14]);
+        CHACHA20_QUARTERROUND(st[3], st[7], st[11], st[15]);
+        CHACHA20_QUARTERROUND(st[0], st[5], st[10], st[15]);
+        CHACHA20_QUARTERROUND(st[1], st[6], st[11], st[12]);
+        CHACHA20_QUARTERROUND(st[2], st[7], st[8], st[13]);
+        CHACHA20_QUARTERROUND(st[3], st[4], st[9], st[14]);
+    }
+}
+
+static void chacha20_update(uint8_t out[CHACHA20_BLOCKBYTES], uint32_t st[16])
+{
+    uint32_t ks[16];
+    int i;
+
+    memcpy(ks, st, 4 * 16);
+    CHACHA20_ROUNDS(st);
+    for (i = 0; i < 16; i++) {
+        ks[i] += st[i];
+    }
+    memcpy(out, ks, CHACHA20_BLOCKBYTES);
+    st[12]++;
+}
+
+static void chacha20_init(uint32_t st[16], const uint8_t key[CHACHA20_KEYBYTES])
+{
+    static const uint32_t constants[4] = { 0x61707865, 0x3320646e, 0x79622d32, 0x6b206574 };
+    memcpy(&st[0], constants, 4 * 4);
+    memcpy(&st[4], key, CHACHA20_KEYBYTES);
+    memset(&st[12], 0, 4 * 4);
+}
+
+static int chacha20_rng(uint8_t* out, size_t len, uint8_t key[CHACHA20_KEYBYTES])
+{
+    uint32_t st[16];
+    size_t off;
+
+    chacha20_init(st, key);
+    chacha20_update(&out[0], st);
+    memcpy(key, out, CHACHA20_KEYBYTES);
+    off = 0;
+    while (len >= CHACHA20_BLOCKBYTES) {
+        chacha20_update(&out[off], st);
+        len -= CHACHA20_BLOCKBYTES;
+        off += CHACHA20_BLOCKBYTES;
+    }
+    if (len > 0) {
+        uint8_t tmp[CHACHA20_BLOCKBYTES];
+        chacha20_update(tmp, st);
+        memcpy(&out[off], tmp, len);
+    }
+    return 0;
+}
+
+struct rng_state {
+    int initialized;
+    size_t off;
+    uint8_t key[CHACHA20_KEYBYTES];
+    uint8_t reserve[RNG_RESERVE_LEN];
+};
+
+void arc4random_buf(void* buffer, size_t len)
+{
+    static _Thread_local struct rng_state rng_state;
+
+    unsigned char* buffer_ = (unsigned char*)buffer;
+    size_t off;
+    size_t remaining;
+    size_t partial;
+
+    if (!rng_state.initialized) {
+        if (getentropy(rng_state.key, sizeof rng_state.key) != 0) {
+            assert(0);
+        }
+        rng_state.off = RNG_RESERVE_LEN;
+        rng_state.initialized = 1;
+    }
+    off = 0;
+    remaining = len;
+    while (remaining > 0) {
+        if (rng_state.off == RNG_RESERVE_LEN) {
+            while (remaining >= RNG_RESERVE_LEN) {
+                chacha20_rng(&buffer_[off], RNG_RESERVE_LEN, rng_state.key);
+                off += RNG_RESERVE_LEN;
+                remaining -= RNG_RESERVE_LEN;
+            }
+            if (remaining == 0) {
+                break;
+            }
+            chacha20_rng(&rng_state.reserve[0], RNG_RESERVE_LEN, rng_state.key);
+            rng_state.off = 0;
+        }
+        partial = RNG_RESERVE_LEN - rng_state.off;
+        if (remaining < partial) {
+            partial = remaining;
+        }
+        memcpy(&buffer_[off], &rng_state.reserve[rng_state.off], partial);
+        memset(&rng_state.reserve[rng_state.off], 0, partial);
+        rng_state.off += partial;
+        remaining -= partial;
+        off += partial;
+    }
+}
+
+uint32_t arc4random(void)
+{
+    uint32_t v;
+
+    arc4random_buf(&v, sizeof v);
+
+    return v;
+}
+
+uint32_t arc4random_uniform(const uint32_t upper_bound)
+{
+    uint32_t min;
+    uint32_t r;
+
+    if (upper_bound < 2U) {
+        return 0;
+    }
+    min = (1U + ~upper_bound) % upper_bound; // = 2**32 mod upper_bound
+    do {
+        r = arc4random();
+    } while (r < min);
+
+    // r is now clamped to a set whose size mod upper_bound == 0.
+    // The worst case (2**31+1) requires 2 attempts on average.
+
+    return r % upper_bound;
+}