Better defaults for ipfs key export (PEM, PKCS)

[lidel]

Current implementation

Right now, the ipfs key export -o foo.key just spits out the key in proprietary Protobuf, without any protection:

• https://github.com/ipfs/go-ipfs/blob/8cfc88961d4081b2749fba135b63ffcca5a62456/core/commands/keystore.go#L189
• https://github.com/libp2p/go-libp2p-core/blob/1262f601475277211be0af5527932f6e5aa87313/crypto/key.go#L245

This is not only a dangerous default, but makes it difficult to interop with the outside world.
People building on IPFS asked for the ability to generate keys outside go-ipfs and/or export them in a form that is useful out of the box, or a safer way to export a key to move it to a different box.

Ref. https://discuss.ipfs.io/t/importing-pem-encoded-private-key/12770/9

Proposed fix

We should fix the default behavior and do what js-ipfs does:

ipfs.key.export(name, password, [options]):
Export a key in a PEM encoded password protected PKCS 8

Namely:

• never export unencrypted keys by default
• leverage well-established open standards to maximize interoperability and improve devexp

Some implementation suggestions:

• change the default to produce something like well-established PEM 8 (https://en.wikipedia.org/wiki/PKCS)
• make --format=pem-pkcs8-encrypted the implicit default
  • this ensures the default is sane: requires password and produces encrypted key
  • it is ok to allow unencrypted export via explicit opt-in --format=pem-pkcs8-cleartext
• handle legacy format: allow users to export to the old format via something like --format=libp2p-protobuf-cleartext
• import should be smart enough to detect the key format based on a few first bytes, but it should also take explicit --format and return error if input does not match expected format

---

Update: turns out js-ipfs uses PEM only for RSA keys, Ed25519 (current default) use custom format encrypted with aes-gcm (details in #8616 (review)) – I suggested focussing on cleartext (unencrypted) PEM for now, as it the most interoperable with external software.

[lidel]

Turns out js-ipfs uses PEM only for RSA keys, Ed25519 keys (current default) use custom format encrypted with aes-gcm (details in #8616 (review))
Due to this, we are focussing on cleartext (unencrypted) PEM for now, as it the most interoperable with external software, and we will not be changing any defaults at this time. Such decision requires cleaning up interop with js-ipfs first.

👉 Opt-in support for keys in cleartext PEM files is being implemented in #8616, this should be enough to allow cool interop with other software: using IPFS keys in other apps, or generating (deriving) a key by a third party app and then importing and using it for IPNS.

[schomatis]

Done in #8616.