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Tests and cleanup #241

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merged 4 commits into from
Oct 10, 2024
Merged

Tests and cleanup #241

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a025f78
Add some context to error handling in test cases.
flihp Oct 9, 2024
cb3a756
Add negative test cases for share verification failure.
flihp Oct 10, 2024
b89ecd9
Add constant for length of Share.
flihp Oct 10, 2024
144102c
use a constant for the file name used for the serialized verifier
flihp Oct 10, 2024
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85 changes: 60 additions & 25 deletions src/hsm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,9 @@ const DOMAIN: Domain = Domain::all();
const ID: Id = 0x1;
const SEED_LEN: usize = 32;
const KEY_LEN: usize = 32;
const SHARE_LEN: usize = KEY_LEN + 1;
const LABEL: &str = "backup";
const VERIFIER_FILE: &str = "verifier.json";

const SHARES: usize = 5;
const THRESHOLD: usize = 3;
Expand Down Expand Up @@ -229,11 +231,11 @@ impl Hsm {
Scalar,
ProjectivePoint,
ChaCha20Rng,
{ KEY_LEN + 1 },
SHARE_LEN,
>(*nzs.as_ref(), None, &mut rng)
.map_err(|e| HsmError::SplitKeyFailed { e })?;

let verifier_path = self.out_dir.join("verifier.json");
let verifier_path = self.out_dir.join(VERIFIER_FILE);
debug!(
"Serializing verifier as json to: {}",
verifier_path.display()
Expand Down Expand Up @@ -424,18 +426,15 @@ impl Hsm {
info!("Restoring HSM from backup");
info!("Restoring backup / wrap key from shares");
// vector used to collect shares
let mut shares: Vec<Share<{ KEY_LEN + 1 }>> = Vec::new();
let mut shares: Vec<Share<SHARE_LEN>> = Vec::new();

// deserialize verifier:
// verifier was serialized to output/verifier.json in the provisioning ceremony
// it must be included in and deserialized from the ceremony inputs
let verifier = self.out_dir.join("verifier.json");
let verifier = self.out_dir.join(VERIFIER_FILE);
let verifier = fs::read_to_string(verifier)?;
let verifier: FeldmanVerifier<
Scalar,
ProjectivePoint,
{ KEY_LEN + 1 },
> = serde_json::from_str(&verifier)?;
let verifier: FeldmanVerifier<Scalar, ProjectivePoint, SHARE_LEN> =
serde_json::from_str(&verifier)?;

// get enough shares to recover backup key
for _ in 1..=THRESHOLD {
Expand Down Expand Up @@ -499,7 +498,7 @@ impl Hsm {
};

// construct a Share from the decoded hex string
let share: Share<{ KEY_LEN + 1 }> =
let share: Share<SHARE_LEN> =
match Share::try_from(&share_vec[..]) {
Ok(share) => share,
Err(_) => {
Expand Down Expand Up @@ -536,7 +535,7 @@ impl Hsm {

let scalar = Feldman::<THRESHOLD, SHARES>::combine_shares::<
Scalar,
{ KEY_LEN + 1 },
SHARE_LEN,
>(&shares)
.map_err(|e| HsmError::CombineKeyFailed { e })?;

Expand Down Expand Up @@ -936,13 +935,15 @@ mod tests {
secret
}

fn deserialize_share(share: &str) -> Result<Share<{ KEY_LEN + 1 }>> {
fn deserialize_share(share: &str) -> Result<Share<SHARE_LEN>> {
// filter out whitespace to keep hex::decode happy
let share: String =
share.chars().filter(|c| !c.is_whitespace()).collect();
let share = hex::decode(share)?;
let share = hex::decode(share)
.context("failed to decode share from hex string")?;

Ok(Share::try_from(&share[..])?)
Ok(Share::try_from(&share[..])
.context("Failed to construct Share from bytes.")?)
}

#[test]
Expand All @@ -958,7 +959,7 @@ mod tests {
Scalar,
ProjectivePoint,
ThreadRng,
{ KEY_LEN + 1 },
SHARE_LEN,
>(*nzs.as_ref(), None, &mut rng)
.map_err(|e| anyhow::anyhow!("failed to split secret: {}", e))?;

Expand All @@ -968,7 +969,7 @@ mod tests {

let scalar = Feldman::<THRESHOLD, SHARES>::combine_shares::<
Scalar,
{ KEY_LEN + 1 },
SHARE_LEN,
>(&shares)
.map_err(|e| anyhow::anyhow!("failed to combine secret: {}", e))?;

Expand All @@ -984,13 +985,9 @@ mod tests {
// deserialize a verifier & use it to verify the shares in SHARE_ARRAY
#[test]
fn verify_shares() -> Result<()> {
use vsss_rs::FeldmanVerifier;

let verifier: FeldmanVerifier<
Scalar,
ProjectivePoint,
{ KEY_LEN + 1 },
> = serde_json::from_str(VERIFIER)?;
let verifier: FeldmanVerifier<Scalar, ProjectivePoint, SHARE_LEN> =
serde_json::from_str(VERIFIER)
.context("Failed to deserialize FeldmanVerifier from JSON.")?;

for share in SHARE_ARRAY {
let share = deserialize_share(share)?;
Expand All @@ -1000,16 +997,54 @@ mod tests {
Ok(())
}

#[test]
fn verify_zero_share() -> Result<()> {
let verifier: FeldmanVerifier<Scalar, ProjectivePoint, SHARE_LEN> =
serde_json::from_str(VERIFIER)
.context("Failed to deserialize FeldmanVerifier from JSON.")?;

let share: Share<SHARE_LEN> =
Share::try_from([0u8; SHARE_LEN].as_ref())
.context("Failed to create Share from static array.")?;

assert!(!verifier.verify(&share));

Ok(())
}

// TODO: I had expected that changing a single bit in a share would case
// the verifier to fail but that seems to be very wrong.
#[test]
fn verify_share_with_changed_byte() -> Result<()> {
let verifier: FeldmanVerifier<Scalar, ProjectivePoint, SHARE_LEN> =
serde_json::from_str(VERIFIER)
.context("Failed to deserialize FeldmanVerifier from JSON.")?;

let mut share = deserialize_share(SHARE_ARRAY[0])?;
println!("share: {}", share.0[0]);
share.0[1] = 0xff;
share.0[2] = 0xff;
share.0[3] = 0xff;
// If we don't change the next byte this test will start failing.
// I had (wrongly?) expected that the share would fail to verify w/
// a single changed byte
share.0[4] = 0xff;

assert!(!verifier.verify(&share));

Ok(())
}

#[test]
fn recover_secret() -> Result<()> {
let mut shares: Vec<Share<{ KEY_LEN + 1 }>> = Vec::new();
let mut shares: Vec<Share<SHARE_LEN>> = Vec::new();
for share in SHARE_ARRAY {
shares.push(deserialize_share(share)?);
}

let scalar = Feldman::<THRESHOLD, SHARES>::combine_shares::<
Scalar,
{ KEY_LEN + 1 },
SHARE_LEN,
>(&shares)
.map_err(|e| anyhow::anyhow!("failed to combine secret: {}", e))?;

Expand Down
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