This project is an initiative of NCC What are multi-signature transactions?. It is an open and collaborative project to join efforts in discovering smart contract vulnerabilities within the security community. The Reentrancy attack, probably the most famous Ethereum vulnerability, surprised everyone when discovered for the first time.
It was first unveiled during a multimillion dollar heist which led to a hard fork of Ethereum. Reentrancy occurs when external contract calls are allowed to make new calls to the calling contract before the initial execution is complete. The following function contains a function vulnerable to a reentrancy attack. Access Control issues are common in all programs, not just smart contracts.
In fact, it’s number 5 on the OWASP top 10. One usually accesses a contract’s functionality through its public or external functions. This is a common pattern for granting special privileges such as the ability to withdraw the contract’s funds. Unfortunately, the initialization function can be called by anyone — even after it has already been called.
Allowing anyone to become the owner of the contract and take its funds. In the following example, the contract’s initialization function sets the caller of the function as its owner. However, the logic is detached from the contract’s constructor, and it does not keep track of the fact that it has already been called. In the Parity multi-sig wallet, this initialization function was detached from the wallets themselves and defined in a “library” contract. Unfortunately, as in our example, the function did not check if the wallet had already been initialized.
If overflows occur, many benign-seeming codepaths become vectors for theft or denial of service. The resulting balance underflows and becomes an order of magnitude larger than it should be. The fourth example features the soon-to-be-deprecated var keyword. Because var will change itself to the smallest type needed to contain the assigned value, it will become an uint8 to hold the value 0. It can lead to unexpected behavior if return values are not handled properly. Instead, they will return a boolean value set to false, and the code will continue to run. EVM will replace its return value with false.
Denial of service is deadly in the world of Ethereum: while other types of applications can eventually recover, smart contracts can be taken offline forever by just one of these attacks. The auction contract will store the ether in escrow until the object’s owner accepts the bid or the initial bidder cancels it. This means that the auction contract must hold the full value of any unresolved bid in its balance. As the function sends the amount to a hardcoded address, the developers have decided to make the function public. This destroys the promise of escrow and blocks all the pending bids.
Unfortunately, if the previous president is a smart contract and causes reversion on payment, the transfer of power will fail and the malicious smart contract will remain president forever. In this second example, a caller can decide who the next function call will reward. 400 ETH being lost to an unknown player who waited for 256 blocks before revealing the predictable winning number. Randomness is hard to get right in Ethereum. While Solidity offers functions and variables that can access apparently hard-to-predict values, they are generally either more public than they seem or subject to miners’ influence. In this first example, a private seed is used in combination with an iteration number and the keccak256 hash function to determine if the caller wins. Eventhough the seed is private, it must have been set via a transaction at some point in time and it is thus visible on the blockchain.
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Turns out, all it takes is about 150 lines of Python to get a working front-running algorithm. Since the Ethereum blockchain is public, everyone can see the contents of others’ pending transactions. 1 and prime2 rewards the caller. Alice successfuly factors the RSA number and submits a solution.
The second transaction gets picked up first by miners due to the higher paid fee. From locking a token sale to unlocking funds at a specific time for a game, contracts sometimes need to rely on the current time. This is usually done via block. But where does that value come from? Because a transaction’s miner has leeway in reporting the time at which the mining occurred, good smart contracts will avoid relying strongly on the time advertised. A bit before midnight the miner ends up mining the block.
The following function only accepts calls that come after a specific date. Short address attacks are a side-effect of the EVM itself accepting incorrectly padded arguments. Attackers can exploit this by using specially-crafted addresses to make poorly coded clients encode arguments incorrectly before including them in transactions. Is this an EVM issue or a client issue?
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Should it be fixed in smart contracts instead? While everyone has a different opinion, the fact is that a great deal of ether could be directly impacted by this issue. An exchange API has a trading function that takes a recipient address and an amount. Alice to transfer him 20 tokens. He maliciously gives her his address truncated to remove the trailing zeroes. The API pads the address with 12 zero bytes, making it 31 bytes instead of the 32 bytes. Effectively stealing one byte from the following _amount argument.
Eventually, the EVM executing the smart contract’s code will remark that the data is not properly padded and will add the missing byte at the end of the _amount argument. Effectively transfering 256 times more tokens than thought. The main problem was that reviewers did not know what to look for. Ethereum is still in its infancy.
The main language used to develop smart contracts, Solidity, has yet to reach a stable version and the ecosystem’s tools are still experimental. Some of the most damaging smart contract vulnerabilities surprised everyone, and there is no reason to believe there will not be another one that will be equally unexpected or equally destructive. How and Why to Complete Your Stellar. Transactions are commands that modify the ledger state.
Among other things, Transactions are used to send payments, enter orders into the distributed exchange, change settings on accounts, and authorize another account to hold your currency. Source account This is the account that originates the transaction. The transaction must be signed by this account, and the transaction fee must be paid by this account. The sequence number of this transaction is based off this account. Fee Each transaction sets a fee that is paid by the source account. If this fee is below the network minimum the transaction will fail.
The more operations in the transaction, the greater the required fee. Sequence number Each transaction has a sequence number. Transactions follow a strict ordering rule when it comes to processing of transactions per account. For the transaction to be valid, the sequence number must be 1 greater than the sequence number stored in the source account entry when the transaction is applied. Note that if several transactions with the same source account make it into the same transaction set, they are ordered and applied according to sequence number. For example, if 3 transactions are submitted and the account is at sequence number 5, the transactions must have sequence numbers 6, 7, and 8.
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List of operations Transactions contain an arbitrary list of operations inside them. Operations are executed in order as one ACID transaction, meaning that either all operations are applied or none are. If any operation fails, the whole transaction fails. List of signatures Up to 20 signatures can be attached to a transaction.
A transaction is considered invalid if it includes signatures that aren’t needed to authorize the transaction—superfluous signatures aren’t allowed. Memo optional The memo contains optional extra information. It is the responsibility of the client to interpret this value. MEMO_TEXT : A string encoded using either ASCII or UTF-8, up to 28-bytes long. MEMO_ID : A 64 bit unsigned integer. MEMO_HASH : A 32 byte hash.
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MEMO_RETURN : A 32 byte hash intended to be interpreted as the hash of the transaction the sender is refunding. If a transaction is submitted too early or too late, it will fail to make it into the transaction set. Time equal 0 means that it’s not set. Transaction sets Between ledger closings, all the nodes in the network are collecting transactions. When it is time to close the next ledger, the nodes collect these transactions into a transaction set. SCP is run by the network to reach agreement on which transaction set to apply to the last ledger. Signing: Once the transaction is filled out, all the needed signatures must be collected and added to the transaction envelope.
Commonly it’s just the signature of the account doing the transaction, but more complicated setups can require collecting signatures from multiple parties. Submitting: After signing, the transaction should be valid and can now be submitted to the Stellar network. Transactions are typically submitted using horizon, but you can also submit the transaction directly to an instance of stellar-core. Propagating: Once stellar-core receives a transaction, either given to it by a user or another stellar-core, it does preliminary checks to see if the transaction is valid. Among other checks, it makes sure that the transaction is correctly formed and the source account has enough to cover the transaction fee.
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Stellar-core doesn’t check things that require inspecting the state of the ledger beyond looking up the source account—e. Including in a transaction set: When it’s time to close the ledger, stellar-core takes all the transactions it has heard about since last ledger close and collects them into a transaction set. If it hears about any incoming transactions now, it puts them aside for next ledger close. Stellar-core nominates the transaction set it has collected. Application: Once SCP agrees on a particular transaction set, that set is applied to the ledger.
At this point, a fee is taken from the source account for every transaction in that set. Operations are attempted in the order they occur in the transaction. If any operation fails, the whole transaction fails, and the effects of previous operations in that transaction are rolled back. Sequence number does not match source account. Fee would bring account below minimum reserve. Our cloud platform lets you integrate with existing business systems quickly and easily, with open APIs that let you build additional functionality and scalability as your needs grow.
We tailor onboarding programs to meet the needs of businesses of all sizes. Digital Transaction Management What is Digital Transaction Management? DTM removes the friction inherent in transactions that involve people, documents, and data to create faster, easier, more convenient, and secure processes. How do electronic signatures fit in with DTM? Electronic signatures are at the core of DTM.
Often times, at the tail end of the process when documents need to be signed, inefficient processes like printing, faxing, scanning, overnighting and data rekeying take over. DTM delivers benefits to organizations of every size, industry, and geography. DTM use cases are broad reaching and include customer-facing applications such as sales agreements or new customer sign-ups, legal documents such as contract agreements and even include supplier agreements. Digital and mobile technologies have made us more globally connected than ever before.
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This connection is driving massive digital transaction volume—volume that is huge today and expanding in variety and speed. Given the huge volume of high value and sensitive transactions in this space, a standard is imperative. This Governing Board is comprised of industry thought leaders and experts. Electronic Signatures and Legality What is an electronic signature? What are electronic signatures used for?
Electronic signatures are used for many kinds of documents and transactions, for both personal and business use. Some examples include contracts and agreements, loans and leases, forms and orders, and many more. Paper processing, printing, filing, mailing and fax. Delivery over Internet eliminates shipping cost. Delivery of mail may take up to several weeks. Missed form or lost paperwork creates further delays. Often requires the presence of a notary.
Encryption and audit trail ensures documents are tamper-evident. What is the difference between an “electronic signature” and a “digital signature? Electronic signatures, e-signatures, are a broad category of methods for signing a record or a document. A digital signature is a type of e-signature that uses a specific technical implementation. Both digital signatures and other e-signature solutions enable you to sign documents and authenticate the signer. But, the purpose, technical implementation, geographical use, and legal and cultural acceptance of digital signatures versus e-signatures varies.
It enables senders to sign documents with an X. Yes, electronic signatures are legally binding in the United States. Are resources available on the history of ESIGN? In 2010, both Houses of Congress passed a resolution at the request of industry leaders, recognizing June 30 as “National ESIGN Day. Industry letter in support of National ESIGN Day: We, the undersigned, are writing to express our support of H. 290, designating June 30th as “National ESIGN Day. Infographic for the History of National ESIGN Day.
Are electronic signatures legal outside the U. In the UK, the equivalent legislation to the ESIGN Act in the USA was also established in 2000, and is called the UK Electronic Communication Act. EC of 13 December 1999 establishes a Community framework for the use of electronic signatures on electronic contracts in the EU. Each Electronic Signature is unique, documentable, encrypted, and tamper-evident. What if I need an on-premises signing solution due to specific industry or regional laws and regulations? For some regulated transactions, your needs may be best met with an on-premises signing solution that uses digital signature technology. We offer free 30-day trials to help you learn the ropes before you decide if you want to purchase a plan.
You can sign up for a free 30-day trial at our sign-up page. You can log back into your trial account and look for the upgrade button in the upper-right corner of the screen—from there, you’ll be able to complete your purchase. What options do I have for plans and packages? For instance, how many people will be sending envelopes? How complicated are your workflows and compliance? Here are some quick pointers on which plan might work best for you.