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[zk-token-sdk] Limit max seed length for key derivations #33700

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merged 4 commits into from
Oct 20, 2023
Merged

[zk-token-sdk] Limit max seed length for key derivations #33700

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5190bdc
limit max seed length for elgamal keypairs
samkim-crypto Oct 15, 2023
3e47328
limit max seed length for authenticated encryption keys
samkim-crypto Oct 15, 2023
587997e
Apply suggestions from code review
samkim-crypto Oct 20, 2023
45e502d
rename `SeedLengthTooLarge` to `SeedLengthTooLong`
samkim-crypto Oct 20, 2023
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18 changes: 18 additions & 0 deletions zk-token-sdk/src/encryption/auth_encryption.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,8 @@ pub enum AuthenticatedEncryptionError {
DerivationMethodNotSupported,
#[error("seed length too short for derivation")]
SeedLengthTooShort,
#[error("seed length too long for derivation")]
SeedLengthTooLarge,
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}

struct AuthenticatedEncryption;
Expand Down Expand Up @@ -172,10 +174,14 @@ impl EncodableKey for AeKey {
impl SeedDerivable for AeKey {
fn from_seed(seed: &[u8]) -> Result<Self, Box<dyn error::Error>> {
const MINIMUM_SEED_LEN: usize = AE_KEY_LEN;
const MAXIMUM_SEED_LEN: usize = 65535;

if seed.len() < MINIMUM_SEED_LEN {
return Err(AuthenticatedEncryptionError::SeedLengthTooShort.into());
}
if seed.len() > MAXIMUM_SEED_LEN {
return Err(AuthenticatedEncryptionError::SeedLengthTooLarge.into());
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Oh sorry, you'll also need this!

Suggested change
return Err(AuthenticatedEncryptionError::SeedLengthTooLarge.into());
return Err(AuthenticatedEncryptionError::SeedLengthTooLong.into());

}

let mut hasher = Sha3_512::new();
hasher.update(seed);
Expand Down Expand Up @@ -278,4 +284,16 @@ mod tests {
let null_signer = NullSigner::new(&Pubkey::default());
assert!(AeKey::new_from_signer(&null_signer, Pubkey::default().as_ref()).is_err());
}

#[test]
fn test_aes_key_from_seed() {
let good_seed = vec![0; 32];
assert!(AeKey::from_seed(&good_seed).is_ok());

let too_short_seed = vec![0; 15];
assert!(AeKey::from_seed(&too_short_seed).is_err());

let too_long_seed = vec![0; 65536];
assert!(AeKey::from_seed(&too_long_seed).is_err());
}
}
9 changes: 9 additions & 0 deletions zk-token-sdk/src/encryption/elgamal.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,8 @@ pub enum ElGamalError {
DerivationMethodNotSupported,
#[error("seed length too short for derivation")]
SeedLengthTooShort,
#[error("seed length too long for derivation")]
SeedLengthTooLarge,
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}

/// Algorithm handle for the twisted ElGamal encryption scheme
Expand Down Expand Up @@ -449,10 +451,14 @@ impl ElGamalSecretKey {
/// Derive an ElGamal secret key from an entropy seed.
pub fn from_seed(seed: &[u8]) -> Result<Self, ElGamalError> {
const MINIMUM_SEED_LEN: usize = ELGAMAL_SECRET_KEY_LEN;
const MAXIMUM_SEED_LEN: usize = 65535;

if seed.len() < MINIMUM_SEED_LEN {
return Err(ElGamalError::SeedLengthTooShort);
}
if seed.len() > MAXIMUM_SEED_LEN {
return Err(ElGamalError::SeedLengthTooLarge);
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Suggested change
return Err(ElGamalError::SeedLengthTooLarge);
return Err(ElGamalError::SeedLengthTooLong);

}
Ok(ElGamalSecretKey(Scalar::hash_from_bytes::<Sha3_512>(seed)))
}

Expand Down Expand Up @@ -1026,6 +1032,9 @@ mod tests {

let too_short_seed = vec![0; 31];
assert!(ElGamalKeypair::from_seed(&too_short_seed).is_err());

let too_long_seed = vec![0; 65536];
assert!(ElGamalKeypair::from_seed(&too_long_seed).is_err());
}

#[test]
Expand Down