feat: add collision resistance for truncated key id#45
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src/amortized_tokens/server.rs
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| if key_store.get(&truncated_token_key_id).await.is_some() { | ||
| continue; | ||
| } | ||
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| key_store.insert(truncated_token_key_id, server).await; |
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I don't think it's critical (like, could just document it), but this is a Time-of-Check-Time-of-Use race condition, and a fix would be to write an atomic insert if absent method on the key_stores.
src/amortized_tokens/server.rs
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| OsRng.fill_bytes(&mut seed); | ||
| self.create_keypair_internal(key_store, &seed, b"PrivacyPass") | ||
| .await | ||
| loop { |
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the other servers have a loop limit, this one does not.
src/private_tokens/server.rs
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| key_store.insert(truncated_token_key_id, server).await; | ||
| return Ok(public_key); | ||
| } | ||
| Err(CreateKeypairError::SeedError) |
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#[error("Seed is too long")] seems sufficiently incorrect that you might want to make a CollisionExhausted maybe?
src/public_tokens/server.rs
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| key_store | ||
| .insert(truncated_token_key_id, key_pair.clone()) | ||
| .await; | ||
| return Ok(key_pair.pk); |
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Instead of cloning the privkey as well, we can just clone out the pubkey
| key_store | |
| .insert(truncated_token_key_id, key_pair.clone()) | |
| .await; | |
| return Ok(key_pair.pk); | |
| let public_key = key_pair.pk.clone(); | |
| key_store | |
| .insert(truncated_token_key_id, key_pair) | |
| .await; | |
| return Ok(public_key); |
src/private_tokens/server.rs
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| let server = Self::server_from_seed(&seed, b"PrivacyPass")?; | ||
| let public_key = server.get_public_key(); | ||
| let truncated_token_key_id = | ||
| truncate_token_key_id(&public_key_to_token_key_id::<CS>(&server.get_public_key())); |
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| truncate_token_key_id(&public_key_to_token_key_id::<CS>(&server.get_public_key())); | |
| truncate_token_key_id(&public_key_to_token_key_id::<CS>(&public_key)); |
src/amortized_tokens/server.rs
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| let server = Self::server_from_seed(&seed, b"PrivacyPass")?; | ||
| let public_key = server.get_public_key(); | ||
| let truncated_token_key_id = | ||
| truncate_token_key_id(&public_key_to_token_key_id::<CS>(&server.get_public_key())); |
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| truncate_token_key_id(&public_key_to_token_key_id::<CS>(&server.get_public_key())); | |
| truncate_token_key_id(&public_key_to_token_key_id::<CS>(&public_key)); |
src/private_tokens/server.rs
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| self.create_keypair_internal(key_store, &seed, b"PrivacyPass") | ||
| .await | ||
| } | ||
| let attempts_limit = 100; |
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maybe make this a constant somewhere, and use the same one for all three servers?
src/private_tokens/server.rs
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| } | ||
| let attempts_limit = 100; | ||
| for _ in 0..attempts_limit { | ||
| let mut seed = vec![0u8; <<CS::Group as Group>::ScalarLen as Unsigned>::USIZE]; |
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You use GenericArray in Amortized Tokens, which puts the seed on the stack. That seems good, but I'd suggest just doing the same thing everywhere, whichever you like.
src/public_tokens/server.rs
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| let mut verified = false; | ||
| for public_key in public_keys { | ||
| if signature | ||
| .verify(&public_key, None, token_input_bytes.clone(), &options) | ||
| .is_ok() | ||
| { | ||
| verified = true; | ||
| break; | ||
| } | ||
| } |
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Maybe this is an opportunity to use iter().any()? Something like:
| let mut verified = false; | |
| for public_key in public_keys { | |
| if signature | |
| .verify(&public_key, None, token_input_bytes.clone(), &options) | |
| .is_ok() | |
| { | |
| verified = true; | |
| break; | |
| } | |
| } | |
| let verified = public_keys.iter().any(|public_key| { | |
| signature.verify(public_key, None, token_input_bytes.clone(), &options).is_ok() | |
| }); |
perhaps we can get rid of the .clone() on each iteration, too? hmmm
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Thanks for the review, @jcjones. Much appreciated! |
2 participants
Fixes #43.