eERC — Encrypted Metadata

Overview

A newer eERC feature lets users send arbitrary-length encrypted metadata alongside a transaction — e.g. a memo, invoice ID, or payment reference — encrypted so only the intended party (and the auditor) can read it. This extends privacy beyond amounts to the context of a payment.

Where it lives

• Contract: EncryptedERC/contracts/metadata/EncryptedMetadata.sol (+ IEncryptedMetadata.sol).
• The metadata is encrypted client-side (like balances) and stored/emitted with the operation; the chain never sees plaintext.

Why it matters for privacy

• Memos without leaks: traditional "memo" fields are plaintext on-chain. Encrypted metadata keeps the reference confidential.
• Confidential invoicing / reconciliation: attach an invoice or order ID readable only by counterparties.
• Auditor visibility preserved: like amounts, metadata can be made decryptable by the auditor for compliance ([[eerc-auditor-compliance]]).

Usage pattern

1. Client encrypts the metadata payload with the recipient's (and auditor's) public key — same key model as balances ([[eerc-cryptography]]).
2. Submit it with the transfer/operation.
3. Recipient decrypts locally with their decryption key ([[eerc-key-management]]).

Check the current @avalabs/ac-eerc-sdk version for the exact metadata helper/params — the feature is newer than the core transfer API. Read EncryptedMetadata.sol and the SDK changelog.

Privacy considerations

• Length leaks. Arbitrary-length payloads can leak via ciphertext size — pad to fixed buckets if size is sensitive.
• Still public who/when. Metadata being encrypted doesn't hide that a tx with metadata occurred between two addresses ([[eerc-privacy-threat-model]]).
• Don't overload metadata with data better kept off-chain entirely.

Common Pitfalls

• Assuming all SDK versions support it. It's a recent addition; verify the installed version.
• Encrypting to the wrong key. Use the recipient's registered public key (and auditor's) — unregistered recipients can't decrypt.

AI Agent Prompt

"Act as an eERC engineer. Add an encrypted memo/invoice reference to a confidential transfer using the EncryptedMetadata module, encrypting to the recipient and auditor, and pad payloads to fixed sizes to avoid length leakage."

References

See references/README.md (EncryptedERC contracts/metadata/, README 'Encrypted Metadata').