From 6c363981c4b8b7a09716095e2b93043ef2a35c8a Mon Sep 17 00:00:00 2001
From: Jean-Michel Picod <jmichel@google.com>
Date: Thu, 20 Feb 2020 15:32:37 +0100
Subject: [PATCH] Better handling of OpenSSL generated keys.
It seems that ECC keys generated by OpenSSL can be between 30 and 33
bytes long whereas OpenSK code expects a fixed size of 32 bytes.
This variation could cause Travis CI to fail but also invalid ECC keys
to be flashed, causing the authenticator to not work.
---
build.rs | 34 ++++++++++++++++++++++++++++------
1 file changed, 28 insertions(+), 6 deletions(-)
diff --git a/build.rs b/build.rs
index cac13b5..dfbe063 100644
--- a/build.rs
+++ b/build.rs
@@ -43,15 +43,37 @@ fn main() {
pkey.check_key().unwrap();
assert_eq!(pkey.group().curve_name(), Some(Nid::X9_62_PRIME256V1));
- let mut priv_key = pkey.private_key().to_vec();
- if priv_key.len() == 33 && priv_key[0] == 0 {
- priv_key.remove(0);
- }
- assert_eq!(priv_key.len(), 32);
+ // Private keys generated by OpenSSL have variable size but we only handle
+ // constant size. Serialization is done in big endian so if the size is less
+ // than 32 bytes, we need to prepend with null bytes.
+ // If the size is 33 bytes, this means the serialized BigInt is negative.
+ // Any other size is invalid.
+ let priv_key_hex = pkey.private_key().to_hex_str().unwrap();
+ let priv_key_vec = pkey.private_key().to_vec();
+ let key_len = priv_key_vec.len();
+
+ assert!(
+ key_len >= 30,
+ "Invalid private key (too small): {} ({:#?})",
+ priv_key_hex,
+ priv_key_vec,
+ );
+ assert!(
+ key_len <= 33,
+ "Invalid private key (too big): {} ({:#?})",
+ priv_key_hex,
+ priv_key_vec,
+ );
+
+ // Copy OpenSSL generated key to our vec, starting from the end
+ let mut output_vec = [0u8; 32];
+ let min_key_len = std::cmp::min(key_len, 32);
+ output_vec[32usize.saturating_sub(min_key_len)..]
+ .copy_from_slice(&priv_key_vec[key_len.saturating_sub(min_key_len)..]);
// Create the raw private key out of the OpenSSL data
let mut priv_key_bin_file = File::create(&priv_key_bin_path).unwrap();
- priv_key_bin_file.write_all(&priv_key).unwrap();
+ priv_key_bin_file.write_all(&output_vec).unwrap();
// Convert the PEM certificate to DER and extract the serial for AAGUID
let input_pem_cert = include_bytes!("crypto_data/opensk_cert.pem");
--
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