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Without the protocol amendment introduced by this commit, an NFT ID can
be reminted in this manner:
1. Alice creates an account and mints an NFT.
2. Alice burns the NFT with an `NFTokenBurn` transaction.
3. Alice deletes her account with an `AccountDelete` transaction.
4. Alice re-creates her account.
5. Alice mints an NFT with an `NFTokenMint` transaction with params:
`NFTokenTaxon` = 0, `Flags` = 9).
This will mint a NFT with the same `NFTokenID` as the one minted in step
1. The params that construct the NFT ID will cause a collision in
`NFTokenID` if their values are equal before and after the remint.
With the `fixNFTokenRemint` amendment, there is a new sequence number
construct which avoids this scenario:
- A new `AccountRoot` field, `FirstNFTSequence`, stays constant over
time.
- This field is set to the current account sequence when the account
issues their first NFT.
- Otherwise, it is not set.
- The sequence of a newly-minted NFT is computed by: `FirstNFTSequence +
MintedNFTokens`.
- `MintedNFTokens` is then incremented by 1 for each mint.
Furthermore, there is a new account deletion restriction:
- An account can only be deleted if `FirstNFTSequence + MintedNFTokens +
256` is less than the current ledger sequence.
- 256 was chosen because it already exists in the current account
deletion constraint.
Without this restriction, an NFT may still be remintable. Example
scenario:
1. Alice's account sequence is at 1.
2. Bob is Alice's authorized minter.
3. Bob mints 500 NFTs for Alice. The NFTs will have sequences 1-501, as
NFT sequence is computed by `FirstNFTokenSequence + MintedNFTokens`).
4. Alice deletes her account at ledger 257 (as required by the existing
`AccountDelete` amendment).
5. Alice re-creates her account at ledger 258.
6. Alice mints an NFT. `FirstNFTokenSequence` initializes to her account
sequence (258), and `MintedNFTokens` initializes as 0. This
newly-minted NFT would have a sequence number of 258, which is a
duplicate of what she issued through authorized minting before she
deleted her account.
---------
Signed-off-by: Shawn Xie <shawnxie920@gmail.com>
The XRP Ledger
The XRP Ledger is a decentralized cryptographic ledger powered by a network of peer-to-peer nodes. The XRP Ledger uses a novel Byzantine Fault Tolerant consensus algorithm to settle and record transactions in a secure distributed database without a central operator.
XRP
XRP is a public, counterparty-free asset native to the XRP Ledger, and is designed to bridge the many different currencies in use worldwide. XRP is traded on the open-market and is available for anyone to access. The XRP Ledger was created in 2012 with a finite supply of 100 billion units of XRP. Its creators gifted 80 billion XRP to a company, now called Ripple, to develop the XRP Ledger and its ecosystem. Ripple uses XRP to help build the Internet of Value, ushering in a world in which money moves as fast and efficiently as information does today.
rippled
The server software that powers the XRP Ledger is called rippled and is available in this repository under the permissive ISC open-source license. The rippled server software is written primarily in C++ and runs on a variety of platforms. The rippled server software can run in several modes depending on its configuration.
Build from Source
Key Features of the XRP Ledger
- Censorship-Resistant Transaction Processing: No single party decides which transactions succeed or fail, and no one can "roll back" a transaction after it completes. As long as those who choose to participate in the network keep it healthy, they can settle transactions in seconds.
- Fast, Efficient Consensus Algorithm: The XRP Ledger's consensus algorithm settles transactions in 4 to 5 seconds, processing at a throughput of up to 1500 transactions per second. These properties put XRP at least an order of magnitude ahead of other top digital assets.
- Finite XRP Supply: When the XRP Ledger began, 100 billion XRP were created, and no more XRP will ever be created. The available supply of XRP decreases slowly over time as small amounts are destroyed to pay transaction costs.
- Responsible Software Governance: A team of full-time, world-class developers at Ripple maintain and continually improve the XRP Ledger's underlying software with contributions from the open-source community. Ripple acts as a steward for the technology and an advocate for its interests, and builds constructive relationships with governments and financial institutions worldwide.
- Secure, Adaptable Cryptography: The XRP Ledger relies on industry standard digital signature systems like ECDSA (the same scheme used by Bitcoin) but also supports modern, efficient algorithms like Ed25519. The extensible nature of the XRP Ledger's software makes it possible to add and disable algorithms as the state of the art in cryptography advances.
- Modern Features for Smart Contracts: Features like Escrow, Checks, and Payment Channels support cutting-edge financial applications including the Interledger Protocol. This toolbox of advanced features comes with safety features like a process for amending the network and separate checks against invariant constraints.
- On-Ledger Decentralized Exchange: In addition to all the features that make XRP useful on its own, the XRP Ledger also has a fully-functional accounting system for tracking and trading obligations denominated in any way users want, and an exchange built into the protocol. The XRP Ledger can settle long, cross-currency payment paths and exchanges of multiple currencies in atomic transactions, bridging gaps of trust with XRP.
Source Code
Here are some good places to start learning the source code:
- Read the markdown files in the source tree:
src/ripple/**/*.md. - Read the levelization document to get an idea of the internal dependency graph.
- In the big picture, the
mainfunction constructs anApplicationImpobject, which implements theApplicationvirtual interface. Almost every component in the application takes anApplication¶meter in its constructor, typically namedappand stored as a member variableapp_. This allows most components to depend on any other component.
Repository Contents
| Folder | Contents |
|---|---|
./bin |
Scripts and data files for Ripple integrators. |
./Builds |
Platform-specific guides for building rippled. |
./docs |
Source documentation files and doxygen config. |
./cfg |
Example configuration files. |
./src |
Source code. |
Some of the directories under src are external repositories included using
git-subtree. See those directories' README files for more details.