TCAP: Transfer Confidential Asset Protocol

TCAP provides private GPRU balance transitions on Solana using blinded tip PDAs and owner-encrypted balance snapshots.

TCAP is the Transfer Confidential Asset Protocol. It provides private balance accounting for governed assets on Solana. TCAP owns the blinded tip and sequence checks. A successful V2 credit advances the tip from one commitment to the next, and the owner maintains private balance state through locally encrypted snapshots.

The live TCAP path is credit-only. Confidential debits and exits are not live and remain proof-gated. Do not attempt to spend or exit from a TCAP tip using the current Devnet release.

TCAP TIN Tip PDA

The TCapTinTipV1 PDA is derived from ['tcap:tin-tip:v1', blindedRootCommitment]. The account stores:

Field	Type	Description
current_commitment	32-byte hash	Current balance commitment
sequence	u64	Strictly increasing transition number
policy_commitment	32-byte hash	Policy binding for accepted transitions
last_nullifier	32-byte hash	Last consumed transition nullifier
frozen	bool	Freeze flag
version	u8	Account version
bump	u8	PDA bump

The tip does NOT store: TIN, privacy-receiving root, seed, plaintext balance, snapshot key, or token account.

Privacy-safe transition: credit_tcap_tin_tip_v2

The credit_tcap_tin_tip_v2 instruction accepts only a TSN PDA authorization and opaque tip-transition fields. It performs the following checks:

• previous_commitment and new_commitment match the expected sequence.
• sequence is the next expected value.
• Token registry ID matches the asset entry.
• policy_commitment matches the tip.
• gpru_scope_commitment matches the TSN PDA authorization.
• The nullifier differs from the tip’s last transition nullifier.
• Slot window is valid.
• Asset entry is active, approved, and unpaused.

If all checks pass, TCAP atomically advances the tip. The emitted event contains only the tip PDA, sequence, compact token ID, and an opaque transition digest. It never exposes payment intent IDs, raw TIN values, balances, or token accounts. The legacy V1 receipt instruction is retained only for migration and must not be used for new transfers.

Encrypted balance snapshots

After a successful credit, the owner device constructs a canonical private balance snapshot and computes its commitment. The snapshot is encrypted using AES-GCM in an EncryptedTCapBalanceSnapshotV1 envelope. The owner-held snapshot key and plaintext never leave the device.

To read a private balance, the owner device:

1. Fetches the public tip commitment and sequence.
2. Locates the matching encrypted snapshot ciphertext by new_commitment.
3. Decrypts locally with the owner snapshot key.
4. Verifies envelope bindings and commitment hash.

Commitment binding rules

TCAP enforces a strict binding between the on-chain tip and the off-chain snapshot:

tip.current_commitment == snapshot.new_commitment
snapshot.new_commitment = SHA256(canonical snapshot record excluding new_commitment)
tip.sequence == snapshot.sequence

This ensures the private snapshot is an exact successor of the on-chain tip state.

TCAP route V2 and TSN CPI

The V2 TSN CPI wrapper passes only the opaque authorization digest, validity window, predecessor/successor commitments, policy, GPRU scope and nullifier. It does not pass an AcceptedIntentV1, epoch commitment, settlement commitment, or TCAP authorization receipt. A GPRU signature alone cannot move custody; the approved TSN program must sign the CPI-derived authorization PDA.

Devnet reference

The TCAP program ID on Devnet is:

TcApT4CytBqvqEDpRYVB7Wfi6aFzmtSZdWvDsq6bp9x

This is the current TCAP program identity. The V2 instruction source has not been proven on Devnet until the upgraded binary is deployed and the V2 authorization proof gate is exercised. Stable-TCAP is Devnet-only, valueless, and not USDC.

Related pages

TCAP Credits

Developer integration with tip states and credit transitions.

Confidential Settlement

Full TSN to TCAP authorization flow and ABI.

Epoch Treasury

How settlement liability is tracked at the treasury layer.

Identity & Routing

TIN, master seed, and GPRU authorization derivation.