[pve-devel] [PATCH common 1/2] encrypt_pw: allow yescrypt in addition to sha256

[Shannon Sterz]

On Mon Mar 31, 2025 at 12:03 PM CEST, Fabian Grünbichler wrote:
> this has been the default for Debian since Bullseye[0].
>
> besides password setting for the PAM/PVE/PMG realms, this is also used
> to hash cloud-init passwords for Linux VMs, where only a subset of
> prefixes is currently allowed.
>
> 'j9T' is the default cost factor for yescrypt.
>
> 0: https://www.debian.org/releases/bullseye/amd64/release-notes/ch-information.en.html#pam-default-password
>
> Signed-off-by: Fabian Grünbichler <f.gruenbichler at proxmox.com>
> ---
>
> Notes:
>     instead of opt-in to yescrypt, we could also default to it and opt-into sha256
>     in qemu-server for cloud init.. but that means breaking old qemu-server, as
>     opposed to the change being completely backwards compatible..
>
>  src/PVE/Tools.pm | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/src/PVE/Tools.pm b/src/PVE/Tools.pm
> index 57eb86c..95cd93c 100644
> --- a/src/PVE/Tools.pm
> +++ b/src/PVE/Tools.pm
> @@ -1805,7 +1805,7 @@ sub fchownat($$$$$) {
>  my $salt_starter = time();
>
>  sub encrypt_pw {
> -    my ($pw) = @_;
> +    my ($pw, $prefix) = @_;
>
>      $salt_starter++;
>      my $salt = substr(Digest::SHA::sha1_base64(time() + $salt_starter + $$), 0, 8);
> @@ -1813,7 +1813,18 @@ sub encrypt_pw {
>      # crypt does not want '+' in salt (see 'man crypt')
>      $salt =~ s/\+/X/g;
>
> -    return crypt(encode("utf8", $pw), "\$5\$$salt\$");
> +    $prefix = '5' if !$prefix;
> +
> +    my $input;
> +    if ($prefix eq '5') {
> +        $input = "\$5\$$salt\$";
> +    } elsif ($prefix eq 'y') {
> +        $input = "\$y\$j9T\$$salt\$"

since you already mentioned that switching to proxmox-sys via perl mod
might be an option, one thing to point out is that it already also
provides a wrapper for `man 3 crypt_gensalt` for generating the proper
cost factor the same way Debian does instead of hardcoding it as
`j9T` here. it would make it easier to keep that in-sync.

> +    } else {
> +        die "Cannot hash password, unknown crypt prefix '$prefix'\n";
> +    }
> +
> +    return crypt(encode("utf8", $pw), $input);
>  }
>
>  # intended usage: convert_size($val, "kb" => "gb")