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[confidential-transfer] Add confidential transfer ciphertext arithmetic crate #7026
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joncinque
approved these changes
Jul 18, 2024
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| // Unfortunately, the `solana-zk-sdk` does not exporse a constructor interface | ||
| // to construct `PodRistrettoPoint` from bytes. As a work-around, encode the | ||
| // bytes as base64 string and then convert the string to a | ||
| // `PodElGamalCiphertext`. | ||
| let ciphertext_string = STANDARD.encode(ciphertext_bytes); | ||
| FromStr::from_str(&ciphertext_string).unwrap() |
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Is it worth adding the constructor in future work? This seems a bit strange
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Yes, we should add the constructor on the zk-sdk side. I'l create an issue on the SPL side to use the new constructor once it lands.
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Problem
The syscall ElGamal ciphertext arithmetic functions (the logic in
solana_zk_token_sdk::zk_elgamal::ops) have been removed insolana-zk-sdkas they are related specifically to the token program with plans to be moved into the spl repo.Summary of changes
Added the confidential transfer
ciphertext-arithmeticcrate that implements the syscall ElGamal ciphertext arithmetic functions.This is essentially a copy of the logic from
solana_zk_token_sdk::zk_elgamal::opsexcept for the following functions:elgamal_ciphertext_to_ristretto(...): In thezk-token-sdk,(PodPedersenCommitment, PodDecryptHandle)implementedTryFromforPodElGamalCiphertext. However, this was removed inzk-sdkfor simplicity. Theelgamal_ciphertext_to_ristretto(...)was added as a function to directly convert from these two types. The return type is actually(PodRistrettoPoint, PodRistrettoPoint)becausePodRistrettoPoint` is actually the type that is used in the syscall functions.ristretto_to_elgamal_ciphertext(...): This function is the opposite/complement of the function above. Unfortunately, there is one complication with this function. Insolana-zk-token-sdk, thePodElGamalCiphertextis defined asPodElGamalCiphertext(pub [u8; 64]). However, insolana-zk-sdk, we havePodElGamalCiphertext(pub(crate) [u8; 64])and it does not expose a constructor that allows us to createPodElGamalCiphertextfrom array bytes directly. As a workaround, I ended up converting array bytes into base64 strings and then converting it toPodElGamalCiphertext, sincePodElGamalCiphertextdoes implementFromStr... I think we can use this workaround for now until the next major agave release where we add a proper constructor insolana-zk-sdk.