# Kosakata

## Kosakata

**Host chain** \
The chain on which TBTC is minted 

**Keep** \
Secure multiparty computation setups powering tBTC signing

**PKH** \
Public key hash 

Random beacon \
A secure, verifiable source of randomness accessible on the host chain. 

### tBTC

\
**Deposit** \
A deposit is the core component in the system architecture. Each deposit represents a set of bonded signers that generate a Bitcoin public key and accept a single Bitcoin UTXO, from which TBTC can be drawn. 

**Deposit beneficiary** \
A deposit has a single beneficiary Ethereum account — originally set to the depositor. The beneficiary owns the right to some fees on deposit redemption. 

**Deposit request** \
A request for signers to be selected and generate a new Bitcoin ECDSA keypair. A successful request yields a new Bitcoin address ready to accept funds as well as a set of bonded signers. 

**Lot size** \
The ideal size of a funded deposit’s BTC UTXO. Standardizing lot sizes across deposits simplifies the BTC redemption process and pricing of deposits by the market. 

**Signing bond** \
The bond signers put up before a deposit is funded. This bond ensures signers will be punished for fraud or poor uptime. 

**Reserved TBTC** \
The amount of TBTC that can’t be drawn from a new deposit. Reserving TBTC on deposit funding sets aside funds to pay signing fee through the deposit term. 

**Cross-chain communication** 

**Consensus relay** \
Chain-tracking SPV on some other chain, e.g. BTCRelay. Consensus relays are long-running crosschain mechanisms that track the consensus state of another chain. They’re distinguished from other uses of the term "relay", eg the "threshold relay" random beacon mechanism. 

**SPV** \
Simplified payment verification 

**Stateless SPV** \
Non-chain-tracking SPV  

### Bitcoin & friends

**P2PKH / P2WPKH** \
Pay to (witness) public key hash 

**P2SH / P2WSH** \
Pay to (witness) script hash 

**Sighash**\
Bitcoin signature hash algorithm 

**BIP 143** \
Adopted SegWit sighash proposal 

**ALL** \
Sighash mode committing to all outputs and all inputs 

**SINGLE** \
Sighash mode committing to one output and all inputs 

**ANYONECANPAY** \
Sighash modifier. Changes all or single to commit to only ONE input 

**SACP, singleACP** \
SINGLEANYONECANPAY 

**Hash160** \
Bitcoin hash function rmd160(sha256(message)). Used for PKH commitments in outputs. Used for SH commitments before segwit 

**Hash256** \
Bitcoin hash function sha256(sha256(message)). Used for txids, sighash, merkle trees, and PoW 

**UTXO** \
(unspent) transaction output 

**Weight unit** \
a measure of bitcoin transaction size. Main transaction info is 4 weight units per byte. Witness info is 1 weight unit per byte 

**Vbyte** \
4 weight units 

**Outpoint** \
A 36-byte string that uniquely identifies Bitcoin UTXOs. It consists of the creating transaction’s tx\_id as a 32-byte LE uint256 (because Satoshi was bad), and a 4-byte LE uint32 denoting the UTXO’s position in the creating transaction’s output vector