kernel: dev: Add /dev/random

Introduce a prototype cryptographically secure (?) random number generator.

The RNG uses ChaCha20 seeded with a SipHash-processed entropy pool. Entropy is
collected only at read time and is mixed into the internal pool before each
ChaCha20 reseed. The design is still experimental.

Signed-off-by: Alex Funo <frost@osmora.org>
Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/sys/dev/random/entropy.c b/sys/dev/random/entropy.c
new file mode 100644
index 0000000..d392b9c
--- /dev/null
+++ b/sys/dev/random/entropy.c
@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include <dev/random/entropy.h>
+#include <dev/random/siphash.h>
+
+void
+mix_entropy(struct entropy_pool *ep, const uint8_t *input,
+    size_t input_len, uint32_t input_entropy_bits)
+{
+    char key[16] = {0,1,2,3,4,5,6,7,8,9,0xa,0xb,0xc,0xd,0xe,0xf};
+    uint64_t hash_result;
+    uint8_t buffer[ENTROPY_POOL_SIZE + input_len];
+    memcpy(buffer, ep->pool, ENTROPY_POOL_SIZE);
+    memcpy(buffer + ENTROPY_POOL_SIZE, input, input_len);
+
+    hash_result = siphash24(buffer, sizeof(buffer), key);
+
+    for (int i = 0; i < 8; ++i) {
+        ep->pool[i] ^= (hash_result >> (i * 8)) & 0xFF;
+    }
+
+    ep->entropy_bits += input_entropy_bits;
+    if (ep->entropy_bits > ENTROPY_POOL_SIZE * 8) {
+        ep->entropy_bits = ENTROPY_POOL_SIZE * 8;
+    }
+}