Load key "/path/to/key": invalid format

The path is filled in per invocation. Related wording from the same loader: "unknown or unsupported key type" for corrupted body bytes (both reproduced with OpenSSH on macOS), and "error in libcrypto" on some versions for PEM-level failures.

OpenSSH — ssh, ssh-keygen, ssh-add

What it means

OpenSSH tried to load a private key file and could not parse it in any format it knows (OPENSSH PRIVATE KEY, PKCS#8, legacy PEM). The file is damaged, truncated, in a foreign format like PuTTY's .ppk, or is not a private key at all — this is a file-format failure, before any passphrase or server interaction.

Why it happens

• Copy-paste damaged the key

  common

  Keys moved through chat, email or terminals lose trailing newlines, gain wrapped lines or smart characters, or drop the final dashes. The base64 body of an OPENSSH PRIVATE KEY block is length-sensitive; one lost character invalidates the file. (A missing final newline alone is a classic trigger.)

• PuTTY .ppk file used with OpenSSH

  common

  PuTTY's key format ("PuTTY-User-Key-File-2: ...") is not OpenSSH's. Pointing ssh -i at a .ppk fails exactly here; the key must be converted once.

• Public key where the private key belongs

  common

  ssh -i id_ecdsa.pub (the .pub file), or an authorized_keys line saved as the identity file — the private-key loader finds public-key content and reports invalid format.

• Truncated or partially synced file

  occasional

  A cloud-synced or scp-interrupted key file cut mid-body parses as garbage. Reproduced: truncating a valid key file yields exactly "invalid format".

How to fix it

1. 1.

   Inspect the framing first

   The first and last lines plus a validity probe (-y prints the public key if — and only if — the private key parses) identify the failure class in seconds.

   head -1 ~/.ssh/id_ecdsa      # -----BEGIN OPENSSH PRIVATE KEY-----
   tail -c 50 ~/.ssh/id_ecdsa | xxd | tail -1   # must end with 0a (newline)
   ssh-keygen -y -f ~/.ssh/id_ecdsa             # parses? prints the public key

2. 2.

   Convert PuTTY keys to OpenSSH format

   One-time conversion with puttygen; afterwards the key works with ssh, ssh-add and ssh-agent.

   puttygen key.ppk -O private-openssh -o ~/.ssh/id_converted
   chmod 600 ~/.ssh/id_converted

3. 3.

   Transfer keys losslessly

   Move key files with scp/rsync rather than clipboards, keep permissions at 600, and if the private key is unrecoverable, generate a fresh pair — modern OpenSSH favors Ed25519.

   scp -p old-host:~/.ssh/id_ecdsa ~/.ssh/
   # or start clean:
   ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519

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