Key derivation
This feature can help setup a hierarchical key infrastructure.
mlar provides a subcommand keyderive to deterministically derive sub-keys from a given key along a derivation path (a bit like BIP-32, except children public keys can't be derived from the parent one).
For instance, if one wants to derive the following scheme:
root_key
├──["App X"]── key_app_x
│ └──["v1.2.3"]── key_app_x_v1.2.3
└──["App Y"]── key_app_y
One can use the following commands:
# Create the root key (--seed can be used if this key must be created deterministically)
mlar keygen root_key
# Create App keys
mlar keyderive root_key key_app_x --path-component "App X"
mlar keyderive root_key key_app_y --path-component "App Y"
# Create the v1.2.3 key of App X
mlar keyderive key_app_x key_app_x_v1.2.3 --path-component "v1.2.3"
At this point, let's consider an outage happened and keys have been lost.
One can recover all the keys from the root_key private key.
For instance, to recover the key_app_v1.2.3:
mlar keyderive root_key recovered_key --path-component "App X" --path-component "v1.2.3"
As such, if the App X owner only knows key_app_x, he can recover all of its subkeys, including key_app_v1.2.3 but excluding key_app_y.
WARNING: This scheme does not provide any revocation mechanism. If a parent key is compromised, all of the key in its sub-tree must be considered compromised (ie. all past and futures key that can be obtained from it). The opposite is not true: a parent key remains safe if any of its children key is compromised.