112 lines
3.4 KiB
Rust
112 lines
3.4 KiB
Rust
use hkdf::Hkdf;
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use sha2::Digest;
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use sha2::digest::{BlockInput, FixedOutput, Reset, Update};
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use generic_array::{ GenericArray, ArrayLength };
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use heapless::{ String, consts::* };
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use crate::buffer::TlsBuffer;
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use core::convert::TryFrom;
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#[derive(Debug, Clone)]
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pub struct HkdfLabel<'a> {
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// Length of hash function
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pub length: u16,
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// Label vector: "tls13 " + label
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pub label_length: u8,
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pub label: &'a [u8],
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// Context vector: Hashed message
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pub context_length: u8,
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pub context: &'a [u8],
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}
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// Implementation of Derive-Secret function in RFC8446
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pub fn derive_secret<Hash>(
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hkdf: &Hkdf<Hash>,
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label: &str,
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hash: Hash
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) -> GenericArray<u8, Hash::OutputSize>
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where
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Hash: Update + BlockInput + FixedOutput + Reset + Default + Clone,
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Hash::OutputSize: ArrayLength<u8>,
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{
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// Build a string using heapless
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// label size:
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// prefix: "tls13 " => 6 chars
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// suffix: at most 12 chars as per RFC8446, section 7.1
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let mut label_string: String<U32> = String::new();
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label_string.push_str("tls13 ").unwrap();
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label_string.push_str(label).unwrap();
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let length = u16::try_from(Hash::output_size()).unwrap();
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let label_length = u8::try_from(label_string.len()).unwrap();
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let hkdf_label = HkdfLabel {
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length,
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label_length,
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label: label_string.as_ref(),
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context_length: u8::try_from(length).unwrap(),
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context: &hash.finalize(),
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};
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// Build info from HKDF label using Buffer
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// length: 2 bytes,
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// label_vec: 18 bytes (label) + 1 byte (len)
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// context_vec: 48 bytes for SHA384 + 1 byte (len)
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let mut array = [0; 100];
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let mut buffer = TlsBuffer::new(&mut array);
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buffer.enqueue_hkdf_label(hkdf_label).unwrap();
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let info: &[u8] = buffer.into();
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// Define output key material (OKM), dynamically sized by hash
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let mut okm: GenericArray<u8, Hash::OutputSize> = GenericArray::default();
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hkdf.expand(info, &mut okm).unwrap();
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okm
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}
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// Implementation of HKDF-Expand-Label function in RFC8446
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// Secret is embedded inside hkdf through salt and input key material (IKM)
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pub fn hkdf_expand_label<Hash>(
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hkdf: &Hkdf<Hash>,
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label: &str,
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context: &str,
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okm: &mut [u8],
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)
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where
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Hash: Update + BlockInput + FixedOutput + Reset + Default + Clone,
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{
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// Build a string using heapless
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// label size:
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// prefix: "tls13 " => 6 chars
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// suffix: at most 12 chars as per RFC8446, section 7.1
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let mut label_string: String<U32> = String::new();
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label_string.push_str("tls13 ").unwrap();
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label_string.push_str(label).unwrap();
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let label_length = u8::try_from(label_string.len()).unwrap();
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let context_slice = context.as_bytes();
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let context_length = u8::try_from(context_slice.len()).unwrap();
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let length = u16::try_from(okm.len()).unwrap();
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// Build HKDF label
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let hkdf_label = HkdfLabel {
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length,
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label_length,
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label: label_string.as_ref(),
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context_length: context_length,
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context: context_slice,
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};
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// Build info from HKDF label using Buffer
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// length: 2 bytes,
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// label_vec: 18 bytes (label) + 1 byte (len)
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// context_vec: 48 bytes for SHA384 + 1 byte (len)
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let mut array = [0; 100];
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let mut buffer = TlsBuffer::new(&mut array);
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buffer.enqueue_hkdf_label(hkdf_label).unwrap();
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let info: &[u8] = buffer.into();
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hkdf.expand(info, okm).unwrap();
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}
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