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maximum confidential amount adjustment #127

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Apr 9, 2020
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maximum confidential amount adjustment #127

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770fc7b
maximum confidential amount adjustment
Mar 24, 2020
d3de4d4
refer to 52 bits as default
Mar 25, 2020
f28120d
remove dash
Mar 25, 2020
7630fae
Notes on default max tx amount
Apr 7, 2020
5d1f823
unit clarification
Apr 8, 2020
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10 changes: 4 additions & 6 deletions features/confidential-transactions/index.md
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Expand Up @@ -88,15 +88,13 @@ elements-cli sendrawtransaction $TX

### Limitations

The implementation of Confidential Transactions as it appears in Elements has some important limitations to be aware of.
The implementation of Confidential Transactions, as it appears in Elements, has some important limitations to be aware of.

The implementation only hides a certain number of the digits of the amount of each transaction output, dependent on the range proof's "blinding coverage" at a desired precision level. Subsequently, there is a "minimum confidential amount" around 0.0001, and a "maximum confidential amount" that is 2<sup>32</sup> times the minimum amount.
The implementation only hides a certain number of the digits of the amount of each transaction output, dependent on the range proof's "blinding coverage" at a desired precision level. The default blinding precision is currently 52 bits, which will cover any value up to 2^52 satoshi, which equates to a maximum amount of just over 45 million BTC equivalent units. As the maximum amount that can be transacted is inherited from Bitcoin, and set at 21 million BTC equivalent units, this currently provides cover for all asset transactions.

Digits smaller than the minimum will be revealed to observers; for example, if the minimum is 0.0001, a transaction output of 123.456789 will look like "?.????89". The tiny amount of information about the value leaked in this way is unlikely to be important, but be aware that this could allow observers to "follow" coins by linking subsequent transactions with identical amounts. All values can be rounded to the minimum to avoid revealing information in this way if preferred.
A transaction output larger than the maximum value set by the blinding precision will reveal the order of magnitude of the amount to observers, and will also reveal additional digits at the bottom of the amount, so care must be taken if you alter the default value.

A transaction output larger than the maximum will reveal the order of magnitude of the amount to observers, and will also reveal additional digits at the bottom of the amount.

For example, if the maximum is 500k, then all outputs under that amount will look the same, but an output between 500k and 5M will be visible as such to observers (but not the exact amount within that range), and will also reveal one additional digit of the low end of the amount. Revealing the range in this way could be a very significant privacy leak; splitting such extremely large transactions to keep them under the maximum confidential amount is strongly recommended.
For example, if a user chooses a lower blinding precision than the default in their own Elements implementation, or an increased maximum transaction amount, then all outputs under the limit will look the same, but an output over the amount will be visible as such to observers. Although the exact amount will not be revealed, the order or magnitue over the maximum will. Revealing the range in this way could be a very significant privacy leak; splitting such extremely large transactions to keep them under the maximum confidential amount is strongly recommended.

### Find out more about Confidential Transactions

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