Problema:
Al conectarse por primera vez a un servidor SSH, el cliente OpenSSH solicita confirmar la autenticidad del servidor verificando su huella digital:
$ ssh -o UserKnownHostsFile="/tmp/authtest" -o CheckHostIP=no -l user -p 22 169.254.0.2
The authenticity of host '169.254.0.2 (169.254.0.2)' can't be established.
ECDSA key fingerprint is SHA256:jCl+n/PrVUuU5WxXFX+hg05a98Ih2LHcPcwqnHi6CuA.
Are you sure you want to continue connecting (yes/no/[fingerprint])?
Al lado yesy nohayrecientemente agregadouna tercera opción (es decir [fingerprint]). Lamentablemente, esta tercera opción no ha sidodocumentado, todavía. La idea detrás de esta tercera opción es proporcionar la huella digital (que se recibió fuera de banda) al cliente para continuar.
No pude hacer que esta tercera opción funcionara:
$ ssh-keyscan 169.254.0.2
# 169.254.0.2:22 SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u1
169.254.0.2 ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGnvY9+cwo8BSGgeT2O5RjH5UMZBbAApIG+Py4T9/b0mf0EUiMP9u6fVi9x3ebLrhn1E2rytq1AD6TPRduzw+nA=
# 169.254.0.2:22 SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u1
169.254.0.2 ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9x/X2yDAdEROoeqQGXk+MJFuk0qUtDNiI7Oxigk66RfTZEjhHnKix4X+ZF/l5FOzcdxivwvSckiMEqW78vZ3YfZx4kSbnMnIQnny5mgnIo3U10oBe86KGq8OZX7yilovQp5j0m+M4WtIt3qtAk02KYsLEkxnLAVoO0H+5rTmIxpjsX/SLgkJ2FjE1WvUiPEL8l1+z50/RDrVkfiwsvzSmmjrV5A70BhonFHmDO1wCNlivuAIR4GW0tKgefn4LLwK9MJjIQj6fPxAR0W28SV79kd17RIoTezbXrxku5OTx5zvnRLKltkJoW2d/7jSvnD/OyjfZJLqACVRQvhQmYp3L
# 169.254.0.2:22 SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u1
169.254.0.2 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAgkzMtRx0jXgzyU7mBbS8fZoCk2Ky+PoZsDnmhQUOwI
$ ssh -o UserKnownHostsFile="/tmp/testkeys" -o CheckHostIP=no -l user -p 22 169.254.0.2
The authenticity of host '169.254.0.2 (169.254.0.2)' can't be established.
ECDSA key fingerprint is SHA256:jCl+n/PrVUuU5WxXFX+hg05a98Ih2LHcPcwqnHi6CuA.
Are you sure you want to continue connecting (yes/no/[fingerprint])? SHA256:jCl+n/PrVUuU5WxXFX+hg05a98Ih2LHcPcwqnHi6CuA.
Please type 'yes', 'no' or the fingerprint: [SHA256:jCl+n/PrVUuU5WxXFX+hg05a98Ih2LHcPcwqnHi6CuA.]
Please type 'yes', 'no' or the fingerprint: jCl+n/PrVUuU5WxXFX+hg05a98Ih2LHcPcwqnHi6CuA.
Please type 'yes', 'no' or the fingerprint: [jCl+n/PrVUuU5WxXFX+hg05a98Ih2LHcPcwqnHi6CuA.]
Please type 'yes', 'no' or the fingerprint: AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGnvY9+cwo8BSGgeT2O5RjH5UMZBbAApIG+Py4T9/b0mf0EUiMP9u6fVi9x3ebLrhn1E2rytq1AD6TPRduzw+nA=
Please type 'yes', 'no' or the fingerprint: [AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGnvY9+cwo8BSGgeT2O5RjH5UMZBbAApIG+Py4T9/b0mf0EUiMP9u6fVi9x3ebLrhn1E2rytq1AD6TPRduzw+nA=]
Please type 'yes', 'no' or the fingerprint: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGnvY9+cwo8BSGgeT2O5RjH5UMZBbAApIG+Py4T9/b0mf0EUiMP9u6fVi9x3ebLrhn1E2rytq1AD6TPRduzw+nA=
Please type 'yes', 'no' or the fingerprint: [ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGnvY9+cwo8BSGgeT2O5RjH5UMZBbAApIG+Py4T9/b0mf0EUiMP9u6fVi9x3ebLrhn1E2rytq1AD6TPRduzw+nA=]
Pregunta:
¿Cómo/en qué formato se supone que debo proporcionar la huella digital al cliente SSH?
Información adicional:
Versión del cliente SSH:
$ ssh -V
OpenSSH_8.1p1 Debian-1, OpenSSL 1.1.1d 10 Sep 2019
Clave pública del servidor:
ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGnvY9+cwo8BSGgeT2O5RjH5UMZBbAApIG+Py4T9/b0mf0EUiMP9u6fVi9x3ebLrhn1E2rytq1AD6TPRduzw+nA= root@debian
Clave privada del servidor (que no cunda el pánico: la clave se generó solo para esta pregunta):
-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAaAAAABNlY2RzYS
1zaGEyLW5pc3RwMjU2AAAACG5pc3RwMjU2AAAAQQRp72PfnMKPAUhoHk9juUYx+VDGQWwA
KSBvj8uE/f29Jn9BFIjD/bun1Yvcd3my64Z9RNq8ratQA+kz0Xbs8PpwAAAAqN7iWqPe4l
qjAAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGnvY9+cwo8BSGge
T2O5RjH5UMZBbAApIG+Py4T9/b0mf0EUiMP9u6fVi9x3ebLrhn1E2rytq1AD6TPRduzw+n
AAAAAgOFpyGXQLAz/A9uBxx4KkbDSZ/ZDUTwt3bsVYUr2hxhgAAAALcm9vdEBkZWJpYW4B
AgMEBQ==
-----END OPENSSH PRIVATE KEY-----
Respuesta1
El punto no forma parte de la huella digital.
Entonces la respuesta debería ser:
SHA256:jCl+n/PrVUuU5WxXFX+hg05a98Ih2LHcPcwqnHi6CuA