How to convert ed25519 private key to putty ppk?

Question

I want to convert an ed25519 private key (which is generated by ssh-keygen command) to a ppk file. But I got the error.

Couldn't load private key (unrecognized cipher name)

Can someone help me?

• tested openssh version: OpenSSH_7.6p1, OpenSSL 1.1.0g 2 Nov 2017 and OpenSSH_7.6p1, OpenSSL 1.0.2n 7 Dec 2017 (on CoreOS and ArchLinux docker container)

• tested putty version: 0.70 64bit, 0.70 32bit and snapshot (on windows 10)

My procedure is as follows.

1. Generate an ed25519 private key

# ssh-keygen -t ed25519 -a 100 Generating public/private ed25519 key pair. Enter file in which to save the key (/root/.ssh/id_ed25519): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /root/.ssh/id_ed25519. Your public key has been saved in /root/.ssh/id_ed25519.pub. The key fingerprint is: SHA256:2HfORujStwmC9c91rmDxMbaV9kVMT70gWxnRXAvNrNU root@f46f23bbad55 The key's randomart image is: +--[ED25519 256]--+ |             +X B| |           . +.@E| |            + +.=| |       o   o . o.| |      . S o + +oo| |       o = = +.=o| |      . o = B + o| |         o B = o | |            = ...| +----[SHA256]-----+  # cat .ssh/id_ed25519 -----BEGIN OPENSSH PRIVATE KEY----- b3BlbnNzaC1rZXktdjEAAAAACmFlczI1Ni1jdHIAAAAGYmNyeXB0AAAAGAAAABClhk1367 G8CQYpo/0c7UShAAAAZAAAAAEAAAAzAAAAC3NzaC1lZDI1NTE5AAAAIIJiwIymcly4s66p za/IL3ZNyT5CiMPj0R+/LnMDmABUAAAAoMJIakdbIL7TOAmX8n4xGSrtp8mc/Mr6qimZAZ zGB7iRhNUXT+isPdf0YuC9mh5NbX43ZYFl+/sWdi2hVmJxbGTwrjaSdNzF3ZnSpi/aVlzF t3bUCtdwhHLaLqy9unw0zPHlfcQsB700GS/bf4VKRmm1+imj3cAldUm2RF3VdI0U9/04yX Mj+VBOmevM0i7R/0d6xUFTH3zj99xxeLI2J6A= -----END OPENSSH PRIVATE KEY-----  # cat .ssh/id_ed25519.pub ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIIJiwIymcly4s66pza/IL3ZNyT5CiMPj0R+/LnMDmABU root@f46f23bbad55 

2. Run puttygen.exe on windows and try to import the ed25519 private key (.ssh/id_ed25519)

Couldn't load private key (unrecognized cipher name)

Answer 1

Update 2019-03-20: https://www.chiark.greenend.org.uk/~sgtatham/putty/releases/0.71.html supports these keys

At the time of writing this, the puttygen snapshot from https://www.chiark.greenend.org.uk/~sgtatham/putty/snapshot.html seems to support these keys where 0.70 did not. It's not explicitly mentioned in the changelog.

I tested Development snapshot 2019-01-17.53747ad