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harden swap key generation

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trng entropy rate is low, so get a lot of it before using anything
out of the pool.
This commit is contained in:
bunnie 2024-06-14 16:08:15 +08:00
parent f6fe1143e2
commit f91cab4f5d
1 changed files with 11 additions and 2 deletions
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13
loader/src/platform/cramium/swap.rs
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@ -285,6 +285,7 @@ impl SwapHal {
}
// generate a random key for swap
crate::print!("Generating swap key...");
let mut trng = sce::trng::Trng::new(utralib::generated::HW_TRNG_BASE as usize);
trng.setup_raw_generation(32);
let mut seed = 0u64;
@ -295,9 +296,16 @@ impl SwapHal {
// 1. whiten the existing TRNG data with ChaCha8
// 2. XOR in another 32 bits of TRNG data
// 3. create a new ChaCha8 from the resulting data
for _ in 0..16 {
for _ in 0..128 {
seed = cstrng.next_u64();
seed ^= trng.get_u32().expect("TRNG error") as u64;
for _ in 0..7 {
let next = trng.get_u32().expect("TRNG error");
// crate::print!("{:x?}", next); // uncomment to sanity check TRNG
seed ^= next as u64;
let next = trng.get_u32().expect("TRNG error");
// crate::print!("{:x?}", next); // uncomment to sanity check TRNG
seed ^= (next as u64) << 32;
}
cstrng = ChaCha8Rng::seed_from_u64(seed);
}
// now we might have a properly seeded cryptographically secure TRNG...
@ -305,6 +313,7 @@ impl SwapHal {
for word in dest_key.chunks_mut(core::mem::size_of::<u32>()) {
word.copy_from_slice(&cstrng.next_u32().to_be_bytes());
}
crate::println!("done!");
// safety: buf.data is aligned to 4096-byte boundary and filled with initialized data
let ssh: &SwapSourceHeader =