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1

I read that smart contracts don’t have a private key, so they can’t sign a transaction. My question is: when a smart contract starts a transaction to an EOA, how are we sure that the smart contract made the transaction if it doesn’t sign anything?
I’m new in this world and I'm still studying English, so please forgive the mistakes.
Thanks you

contract-development transactions blockchain addresses accounts

share|improve this question

edited 9 hours ago

shane

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GBisGBis

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add a comment | 

1

I read that smart contracts don’t have a private key, so they can’t sign a transaction. My question is: when a smart contract starts a transaction to an EOA, how are we sure that the smart contract made the transaction if it doesn’t sign anything?
I’m new in this world and I'm still studying English, so please forgive the mistakes.
Thanks you

contract-development transactions blockchain addresses accounts

share|improve this question

edited 9 hours ago

shane

3,43244 gold badges1111 silver badges3232 bronze badges

asked 9 hours ago

GBisGBis

633 bronze badges

New contributor

GBis is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

I read that smart contracts don’t have a private key, so they can’t sign a transaction. My question is: when a smart contract starts a transaction to an EOA, how are we sure that the smart contract made the transaction if it doesn’t sign anything?
I’m new in this world and I'm still studying English, so please forgive the mistakes.
Thanks you

contract-development transactions blockchain addresses accounts

share|improve this question

edited 9 hours ago

shane

3,43244 gold badges1111 silver badges3232 bronze badges

asked 9 hours ago

GBisGBis

633 bronze badges

New contributor

GBis is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 9 hours ago

shane

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asked 9 hours ago

GBisGBis

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New contributor

GBis is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 9 hours ago

shane

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asked 9 hours ago

GBisGBis

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New contributor

GBis is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 9 hours ago

shane

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edited 9 hours ago

shane

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asked 9 hours ago

GBisGBis

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GBis is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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3 Answers
3

active

oldest

votes

2

It's not so much about whether a smart contract has a private key or not; it's more about the fact that smart contracts can't initiate a transaction. All transactions are started by an EOA to either a smart contract or to another EOA.

If a transaction is sent to a contract the contract may include functionality to call another address within the same transaction (be it to another contract or to an EOA). We can always check msg.sender to see where the transaction came from (who was the previous relayer - the very very original sender is visible with tx.origin).

share|improve this answer

answered 8 hours ago

Lauri PeltonenLauri Peltonen

7,90122 gold badges55 silver badges2828 bronze badges

add a comment | 

1

The smart contract can only send a transaction to an EOA if the transaction was initiated by an EOA. Smart contracts cannot initiate a transaction because they do not have a private key and cannot sign a transaction, as you said.

When value is being sent from a smart contract to an EOA, what is really happening is an EOA sending a transaction to the network that tells the smart contract to send value to the other EOA.

share|improve this answer

answered 9 hours ago

shaneshane

3,43244 gold badges1111 silver badges3232 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Thank you for the corrections and for the answer, I have a further doubt, you say: “an EOA sending a transaction to the network that tells the smart contract to send value to the other EOA“, so when the smart contract send value it mades a transaction, right? If true, how miners verify that the transaction is made by the smart contract?
  
  – GBis
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, every value transfer on Ethereum is through a transaction. For example, here is a transaction from an EOA (0x134...) to a contract (0x0d8...) that initiated a transfer of 31.71388712 BAT from the original EOA (0x134...) to a new EOA (0xdda...). Note: the second EOA (0xdda) could have also been a contract as well—it does not matter where the value gets sent to.
  
  – shane
  8 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  So, like in your example, the smart contract “modifies” the original transaction?
  
  – GBis
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  No it does not. The sending EOA creates a transaction and signs it with his private key. This transaction tells the contract how to behave and what to do (it does this in the data field of the transaction). The transaction is never "modified". When the transaction is sent to the network, Ethereum processes what the transaction instructed it to do, which, in this case, was to send tokens to another address.
  
  – shane
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Ok, therefore an eoa sends a transaction to a smart contract and when the miner verifies that transaction runs the code of the contract and in case add the new transaction “made” by the contract? Thank you for your patience and can you tell me where study the implementation of the “protocol”
  
  – GBis
  7 hours ago
  

  
  
  
  

 | 
show 1 more comment

1

Only an EOA can sign and send a transaction. It can be addressed to a contract in which case the contracts functions must run.

A contract's functions can send messages and/or value to other contracts in which case they also run, or to an EOA which just receives because it has no code.

All of this happens approximately instantaneously (after mining) because it is all considered part of a single atomic transaction that must either complete entirely or fail.

Hope it helps.

share|improve this answer

answered 1 hour ago

Rob Hitchens - B9labRob Hitchens - B9lab

32.8k77 gold badges4848 silver badges8888 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So, when i send a transaction to a smart contract, the miner execute the code and, if the smart contract want to send message, the miner add the message transaction?
  
  – GBis
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The miner includes the transaction (inputs) in a block. Every full node runs the transaction to evaluate what it does for themselves. Running the transaction includes interactions with other contracts or EOAs.
  
  – Rob Hitchens - B9lab
  34 mins ago
  

  
  
  
  

add a comment | 

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2

It's not so much about whether a smart contract has a private key or not; it's more about the fact that smart contracts can't initiate a transaction. All transactions are started by an EOA to either a smart contract or to another EOA.

If a transaction is sent to a contract the contract may include functionality to call another address within the same transaction (be it to another contract or to an EOA). We can always check msg.sender to see where the transaction came from (who was the previous relayer - the very very original sender is visible with tx.origin).

share|improve this answer

answered 8 hours ago

Lauri PeltonenLauri Peltonen

7,90122 gold badges55 silver badges2828 bronze badges

add a comment | 

2

It's not so much about whether a smart contract has a private key or not; it's more about the fact that smart contracts can't initiate a transaction. All transactions are started by an EOA to either a smart contract or to another EOA.

If a transaction is sent to a contract the contract may include functionality to call another address within the same transaction (be it to another contract or to an EOA). We can always check msg.sender to see where the transaction came from (who was the previous relayer - the very very original sender is visible with tx.origin).

share|improve this answer

answered 8 hours ago

Lauri PeltonenLauri Peltonen

7,90122 gold badges55 silver badges2828 bronze badges

add a comment | 

It's not so much about whether a smart contract has a private key or not; it's more about the fact that smart contracts can't initiate a transaction. All transactions are started by an EOA to either a smart contract or to another EOA.

If a transaction is sent to a contract the contract may include functionality to call another address within the same transaction (be it to another contract or to an EOA). We can always check msg.sender to see where the transaction came from (who was the previous relayer - the very very original sender is visible with tx.origin).

share|improve this answer

answered 8 hours ago

Lauri PeltonenLauri Peltonen

7,90122 gold badges55 silver badges2828 bronze badges

share|improve this answer

answered 8 hours ago

Lauri PeltonenLauri Peltonen

7,90122 gold badges55 silver badges2828 bronze badges

answered 8 hours ago

Lauri PeltonenLauri Peltonen

7,90122 gold badges55 silver badges2828 bronze badges

answered 8 hours ago

Lauri PeltonenLauri Peltonen

7,90122 gold badges55 silver badges2828 bronze badges

1

The smart contract can only send a transaction to an EOA if the transaction was initiated by an EOA. Smart contracts cannot initiate a transaction because they do not have a private key and cannot sign a transaction, as you said.

When value is being sent from a smart contract to an EOA, what is really happening is an EOA sending a transaction to the network that tells the smart contract to send value to the other EOA.

share|improve this answer

answered 9 hours ago

shaneshane

3,43244 gold badges1111 silver badges3232 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Thank you for the corrections and for the answer, I have a further doubt, you say: “an EOA sending a transaction to the network that tells the smart contract to send value to the other EOA“, so when the smart contract send value it mades a transaction, right? If true, how miners verify that the transaction is made by the smart contract?
  
  – GBis
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, every value transfer on Ethereum is through a transaction. For example, here is a transaction from an EOA (0x134...) to a contract (0x0d8...) that initiated a transfer of 31.71388712 BAT from the original EOA (0x134...) to a new EOA (0xdda...). Note: the second EOA (0xdda) could have also been a contract as well—it does not matter where the value gets sent to.
  
  – shane
  8 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  So, like in your example, the smart contract “modifies” the original transaction?
  
  – GBis
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  No it does not. The sending EOA creates a transaction and signs it with his private key. This transaction tells the contract how to behave and what to do (it does this in the data field of the transaction). The transaction is never "modified". When the transaction is sent to the network, Ethereum processes what the transaction instructed it to do, which, in this case, was to send tokens to another address.
  
  – shane
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Ok, therefore an eoa sends a transaction to a smart contract and when the miner verifies that transaction runs the code of the contract and in case add the new transaction “made” by the contract? Thank you for your patience and can you tell me where study the implementation of the “protocol”
  
  – GBis
  7 hours ago
  

  
  
  
  

 | 
show 1 more comment

1

The smart contract can only send a transaction to an EOA if the transaction was initiated by an EOA. Smart contracts cannot initiate a transaction because they do not have a private key and cannot sign a transaction, as you said.

When value is being sent from a smart contract to an EOA, what is really happening is an EOA sending a transaction to the network that tells the smart contract to send value to the other EOA.

share|improve this answer

answered 9 hours ago

shaneshane

3,43244 gold badges1111 silver badges3232 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Thank you for the corrections and for the answer, I have a further doubt, you say: “an EOA sending a transaction to the network that tells the smart contract to send value to the other EOA“, so when the smart contract send value it mades a transaction, right? If true, how miners verify that the transaction is made by the smart contract?
  
  – GBis
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, every value transfer on Ethereum is through a transaction. For example, here is a transaction from an EOA (0x134...) to a contract (0x0d8...) that initiated a transfer of 31.71388712 BAT from the original EOA (0x134...) to a new EOA (0xdda...). Note: the second EOA (0xdda) could have also been a contract as well—it does not matter where the value gets sent to.
  
  – shane
  8 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  So, like in your example, the smart contract “modifies” the original transaction?
  
  – GBis
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  No it does not. The sending EOA creates a transaction and signs it with his private key. This transaction tells the contract how to behave and what to do (it does this in the data field of the transaction). The transaction is never "modified". When the transaction is sent to the network, Ethereum processes what the transaction instructed it to do, which, in this case, was to send tokens to another address.
  
  – shane
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Ok, therefore an eoa sends a transaction to a smart contract and when the miner verifies that transaction runs the code of the contract and in case add the new transaction “made” by the contract? Thank you for your patience and can you tell me where study the implementation of the “protocol”
  
  – GBis
  7 hours ago
  

  
  
  
  

 | 
show 1 more comment

The smart contract can only send a transaction to an EOA if the transaction was initiated by an EOA. Smart contracts cannot initiate a transaction because they do not have a private key and cannot sign a transaction, as you said.

When value is being sent from a smart contract to an EOA, what is really happening is an EOA sending a transaction to the network that tells the smart contract to send value to the other EOA.

share|improve this answer

answered 9 hours ago

shaneshane

3,43244 gold badges1111 silver badges3232 bronze badges

share|improve this answer

answered 9 hours ago

shaneshane

3,43244 gold badges1111 silver badges3232 bronze badges

answered 9 hours ago

shaneshane

3,43244 gold badges1111 silver badges3232 bronze badges

answered 9 hours ago

shaneshane

3,43244 gold badges1111 silver badges3232 bronze badges

1

Only an EOA can sign and send a transaction. It can be addressed to a contract in which case the contracts functions must run.

A contract's functions can send messages and/or value to other contracts in which case they also run, or to an EOA which just receives because it has no code.

All of this happens approximately instantaneously (after mining) because it is all considered part of a single atomic transaction that must either complete entirely or fail.

Hope it helps.

share|improve this answer

answered 1 hour ago

Rob Hitchens - B9labRob Hitchens - B9lab

32.8k77 gold badges4848 silver badges8888 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So, when i send a transaction to a smart contract, the miner execute the code and, if the smart contract want to send message, the miner add the message transaction?
  
  – GBis
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The miner includes the transaction (inputs) in a block. Every full node runs the transaction to evaluate what it does for themselves. Running the transaction includes interactions with other contracts or EOAs.
  
  – Rob Hitchens - B9lab
  34 mins ago
  

  
  
  
  

add a comment | 

1

Only an EOA can sign and send a transaction. It can be addressed to a contract in which case the contracts functions must run.

A contract's functions can send messages and/or value to other contracts in which case they also run, or to an EOA which just receives because it has no code.

All of this happens approximately instantaneously (after mining) because it is all considered part of a single atomic transaction that must either complete entirely or fail.

Hope it helps.

share|improve this answer

answered 1 hour ago

Rob Hitchens - B9labRob Hitchens - B9lab

32.8k77 gold badges4848 silver badges8888 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So, when i send a transaction to a smart contract, the miner execute the code and, if the smart contract want to send message, the miner add the message transaction?
  
  – GBis
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The miner includes the transaction (inputs) in a block. Every full node runs the transaction to evaluate what it does for themselves. Running the transaction includes interactions with other contracts or EOAs.
  
  – Rob Hitchens - B9lab
  34 mins ago
  

  
  
  
  

add a comment | 

Only an EOA can sign and send a transaction. It can be addressed to a contract in which case the contracts functions must run.

A contract's functions can send messages and/or value to other contracts in which case they also run, or to an EOA which just receives because it has no code.

All of this happens approximately instantaneously (after mining) because it is all considered part of a single atomic transaction that must either complete entirely or fail.

Hope it helps.

share|improve this answer

answered 1 hour ago

Rob Hitchens - B9labRob Hitchens - B9lab

32.8k77 gold badges4848 silver badges8888 bronze badges

share|improve this answer

answered 1 hour ago

Rob Hitchens - B9labRob Hitchens - B9lab

32.8k77 gold badges4848 silver badges8888 bronze badges

answered 1 hour ago

Rob Hitchens - B9labRob Hitchens - B9lab

32.8k77 gold badges4848 silver badges8888 bronze badges

answered 1 hour ago

Rob Hitchens - B9labRob Hitchens - B9lab

32.8k77 gold badges4848 silver badges8888 bronze badges