openssl – matoken's meme

You can use openssl to generate a shorter key: $ openssl genprsa -out key.pem 768 $ ssh-keygen -y -f key.pem > key.pub # optional to get public key This works with a 768-bit RSA key (client: OpenSSH_7.2p2, OpenSSL 1.0.2g; server: OpenSSH_7.2p2, OpenSSL 1.0.2g) but not a 256-bit RSA key: I can generate the shorter key but the server requires a minimum of 768-bits.

$ openssl genrsa -out id_rsa768 -aes256 768 Generating RSA private key, 768 bit long modulus (2 primes) ..+++++++ ..........+++++++ e is 65537 (0x010001) Enter pass phrase for id_rsa768: Verifying - Enter pass phrase for id_rsa768:

$ openssl genrsa -out id_rsa4096 -aes256 4096 Generating RSA private key, 4096 bit long modulus (2 primes) ................++++ .....................................................................................................++++ e is 65537 (0x010001) Enter pass phrase for id_rsa4096: Verifying - Enter pass phrase for id_rsa4096: $ ssh-keygen -c -C 'OpenSSL generate key' -f ./id_rsa4096 Enter passphrase: No existing comment Comment 'OpenSSL generated key' applied $ ssh-keygen -p -f ./id_rsa4096 Enter old passphrase: Key has comment 'OpenSSL generated key' Enter new passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved with the new passphrase.

$ dpkg-query -W openssl openssh-client openssh-server openssh-client 1:8.1p1-2 openssh-server 1:8.1p1-2 openssl 1.1.1d-2 $ lsb_release -dr Description: Debian GNU/Linux bullseye/sid Release: unstable $ uname -m x86_64

Linux の /etc/shadow のsha512形式の暗号化パスワードを生成するのに OpenSSL を利用したメモです．

最近は SHA512 が規定値になっている

$ grep ^ENCRYPT_METHOD /etc/login.defs
ENCRYPT_METHOD SHA512

openssl passwd は 1.1.1 から sha512 がサポートされている

*) 'openssl passwd' can now produce SHA256 and SHA512 based output,

Changes between 1.1.0i and 1.1.1 [11 Sep 2018]

-6 オプションが SHA512

$ openssl version
OpenSSL 1.1.1a  20 Nov 2018 (Library: OpenSSL 1.1.1b  26 Feb 2019)
$ openssl passwd --help
Usage: passwd [options]
Valid options are:
 -help               Display this summary
 -in infile          Read passwords from file
 -noverify           Never verify when reading password from terminal
 -quiet              No warnings
 -table              Format output as table
 -reverse            Switch table columns
 -salt val           Use provided salt
 -stdin              Read passwords from stdin
 -6                  SHA512-based password algorithm
 -5                  SHA256-based password algorithm
 -apr1               MD5-based password algorithm, Apache variant
 -1                  MD5-based password algorithm
 -aixmd5             AIX MD5-based password algorithm
 -crypt              Standard Unix password algorithm (default)
 -rand val           Load the file(s) into the random number generator
 -writerand outfile  Write random data to the specified file

こんな感じで作れる
$ が区切り文字になっていて， 6 部分が暗号形式のid，SALT 部分がsalt，その後ろが暗号化パスワードになっている

$ openssl passwd -salt SALT -6 PASSWORD
$6$SALT$io0TPmhM8ythCm7Idt0AfYvTuFCLyA1CMVmeT3EUqarf2NQcTuLKEgP9.4Q8fgClzP7OCnyOY1wo1xDw0jtyH1

この文字列を， /etc/shadow の第2フィールドに埋め込むとlogin に利用できる

SALT もランダムにしたい場合は，
/dev/random や

$ tr -cd '[:alnum:]' < /dev/random | head -c 8
ouOpUJoq

openssl rand が使える

$ openssl rand --help
Usage: rand [flags] num
Valid options are:
 -help               Display this summary
 -out outfile        Output file
 -rand val           Load the file(s) into the random number generator
 -writerand outfile  Write random data to the specified file
 -base64             Base64 encode output
 -hex                Hex encode output
 -engine val         Use engine, possibly a hardware device
$ openssl rand -base64 6
Gy/YhLzM

salt 8 文字で sha512 なパスワードを作成

$ openssl passwd -6 -salt $(openssl rand -base64 6) PASSWORD
$6$O2bwYkq/$QIIeAsVueV3vfGZqK/obGMevpB3DwRb/wq2uqn3ykdst1hEV3.72cGPu3gX0p3mD5KPWNrK0M6OPdElDPGD000

実際に /etc/shadow に設定して認証を試してみる

$ sudo useradd testuser
$ sudo sed -i 's,^testuser:[^:]*,testuser:$6$O2bwYkq/$QIIeAsVueV3vfGZqK/obGMevpB3DwRb/wq2uqn3ykdst1hEV3.72cGPu3gX0p3mD5KPWNrK0M6OPdElDPGD000,' /etc/shadow
$ sudo grep ^testuser: /etc/shadow
testuser:$6$O2bwYkq/$QIIeAsVueV3vfGZqK/obGMevpB3DwRb/wq2uqn3ykdst1hEV3.72cGPu3gX0p3mD5KPWNrK0M6OPdElDPGD000:17970:0:99999:7:::
$ su testuser
Password:
$ whoami
testuser
$

openssl のバージョンが古くてSHA512に対応していない場合は適当なscriptで生成できる
salt を同じものにして試すと同じ文字列が得られるのが確認できる

$ perl -e 'print crypt("PASSWORD", ( "\$6$" . "O2bwYkq/" ));'
$6$O2bwYkq/$QIIeAsVueV3vfGZqK/obGMevpB3DwRb/wq2uqn3ykdst1hEV3.72cGPu3gX0p3mD5KPWNrK0M6OPdElDPGD000
$ python -c "import crypt, getpass, pwd; print crypt.crypt('PASSWORD','\$6$O2bwYkq/$')"
$6$O2bwYkq/$QIIeAsVueV3vfGZqK/obGMevpB3DwRb/wq2uqn3ykdst1hEV3.72cGPu3gX0p3mD5KPWNrK0M6OPdElDPGD000

環境

$ dpkg-query -W openssl login
login   1:4.5-1.1
openssl 1.1.1a-1
$ lsb_release -dr
Description:    Debian GNU/Linux buster/sid
Release:        testing
$ uname -m
aarch64

参考URL

タグ: openssl

OpenSSHで使えるRSA鍵ペアをOpenSSLで生成する

OpenSSLでSHA512のPASSWORDを生成する