pkcs1-conv: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/pkcs1-conv - from package: nettle-bin
/usr/lib/debug/usr/bin/pkcs1-conv - from package: nettle-dbg

You may install the required package with command apt-get install {package}
Error in other languages:
pkcs1-conv: bevel nie gevind nie
pkcs1-conv: comandă negăsită
pkcs1-conv: comando não encontrado
pkcs1-conv: commande introuvable
pkcs1-conv: command not found
pkcs1-conv: käsku ei ole
pkcs1-conv: không tìm thấy lệnh
pkcs1-conv: komanda nerasta
pkcs1-conv: Kommando nicht gefunden.
pkcs1-conv: kommandot finns inte
pkcs1-conv: komut yok
pkcs1-conv: nie znaleziono polecenia
pkcs1-conv: níor aimsíodh an t-ordú
pkcs1-conv: no se encontró la orden
pkcs1-conv: no s'ha trobat l'ordre
pkcs1-conv: opdracht niet gevonden
pkcs1-conv: parancs nem található
pkcs1-conv: perintah tidak ditemukan
pkcs1-conv: príkaz nenájdený
pkcs1-conv: příkaz nenalezen
pkcs1-conv: команда не найдена
pkcs1-conv: командата не е открита
pkcs1-conv: 命令找不到
pkcs1-conv: コマンドが見つかりません