Extracting Internal Keys from Bitcoin Transactions
Bitcoin’s private keys are designed to be highly secure and resistant to reverse engineering. One of the challenges in understanding how these keys are generated and used is extracting the internal key from a tweaked-pubkey and bip341 tweak tag.
In this article, we will explore what happens when a user tweaks their public-key using the tweakpubkey command with bip341 and try to extract the internal key. We’ll also discuss why this process seems impossible without more context.
Tweaking a Public Key
When a user wants to tweak their private key, they use the following commands:
$bitcoin-taproot --tweakpubkey
This will modify the private key and generate a new tweaked-pubkey.
The bip341 command is used to specify the tweak tag for the new public key. The tweak tag determines how the user’s private key should be modified to produce the tweaked public key.
Extracting the Internal Key
To extract the internal key from a tweaked-pubkey and bip341 tweak tag, we need to understand how Bitcoin generates these keys.
A Bitcoin transaction consists of a series of input-outputs (IOVs) that are bundled together in a single output. Each IOV contains the sender’s public key, the receiver’s public key, and other relevant information. The internal key is generated by modifying the user’s private key using the tweaked-pubkey.
When a user wants to modify their private key using the tweakpubkey command, Bitcoin generates a new private key that is compatible with the tweak tag specified in the bip341 output. This new private key is then used to sign and verify transactions.
The Problem: Extracting the Internal Key
Now, let’s assume we have a tweaked-pubkey and bip341 tweak tag that allows us to extract the internal key:
$bitcoin-taproot --tweakpubkey 0x00a9d6d5e8c3f4b1abcdef0000000000001
The --tweakpubkey option specifies the tweak tag. The 0x00a9d6d5e8c3f4b1abcdef000000000001 is a sample tweak tag.
To extract the internal key, we can use the bip341 command to generate a new private key that is compatible with this tweaked-pubkey:
$ bitcoin-taproot --tweakpubkey 0x00a9d6d5e8c3f4b1abcdef0000000000001
This will generate a new private key that is compatible with the tweaked-pubkey.
Now, we can use this extracted private key to sign and verify transactions. The internal key is now accessible via the extracted-private-key.
Why Extracting the Internal Key is Impossible without More Context
In summary, extracting the internal key from a tweaked-pubkey and bip341 tweak tag requires more context than just tweaking the public key using tweakpubkey. To extract the internal key, we need to:
- Create a new private key that is compatible with the tweaked-pubkey.
- Use the
bip341command to generate a new private key that matches the tweaked-pubkey’s tweak tag.
Without knowing the exact tweak tag or private key used in the original transaction, it becomes impossible to extract the internal key using just the tweaked-pubkey and bip341 tweak tag.
Conclusion
Tweaking a public-key using tweakpubkey with bip341 can modify the user’s private key, but extracting the internal key from the resulting tweaked-pubkey is not straightforward. Without more context, such as the original transaction or the private key used in the tweaked-pubkey, it seems impossible to extract the internal key.
However, if you have access to the original transaction and the tweaked-pubkey with bip341 tweak tag, you may be able to recover the internal key through reverse engineering.
