Extracting Internal Keys from Bitcoin Transactions
Bitcoin private keys are designed to be very 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 the tweaked-pubkey and bip341 tweak tag.
In this article, we will examine what happens when a user modifies their public key using the tweakpubkey command with bip341 and attempts to extract the internal key. We will also discuss why this process seems impossible without more context.
Tuning the Public Key
When a user wants to set their private key, they will use the following commands:
$ bitcoin-taproot --tweakpubkey
This modifies the private key and generates a new configured pubkey.
The bip341 command is used to specify a tweak tag for a new public key. The tweak tag specifies how the user’s private key should be modified to create a tweaked public key.
Internal Key Extraction
To extract the internal key from the tweaked-pubkey and bip341 tweak tags, we need to understand how Bitcoin generates these keys.
A Bitcoin transaction consists of a series of inputs and outputs (IOVs) that are aggregated into a single output. Each IOV contains the sender’s public key, the recipient’s public key, and other relevant information. The internal key is generated by modifying the user’s private key using 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.
Problem: Extracting the internal key
Now let’s assume we have tweaked-pubkey and a bip341 tweak tag that allows us to extract the internal key:
$ bitcoin-taproot --tweakpubkey 0x00a9d6d5e8c3f4b1abcdef000000000000001
The --tweakpubkey option specifies the tweak tag. 0x00a9d6d5e8c3f4b1abcdef000000000000001 is an example of a 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 0x00a9d6d5e8c3f4b1abcdef00000000000001
This will generate a new private key that is compatible with the tweaked-pubkey.
We can now use this extracted private key to sign and verify transactions. The internal key is now accessible via the `extracted private key''.
Why it is not possible to extract the internal key without additional context
In short, extracting the internal key from tweaked-pubkey and bip341 tweak tags requires more context than just tweaking the public key withtweakpubkey. To extract the internal key, we need to:
- Create a new private key that is compatible with tweaked-pubkey.
- Use thebip341
command to generate a new private key that matches the tweaked-pubkey tweak tag.
Without knowing the exact tweak tag or the private key used in the original transaction, it is impossible to extract the internal key using only the tweaked-pubkey and bip341 tweak tags.
Conclusion
Tweaking a public key usingtweakpubkey` with bip341 can modify a user’s private key, but extracting the internal key from the resulting tweaked public key is not easy. Without additional 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 the tweak tag bip341, you may be able to recover the internal key by reverse engineering.