def build_tlsa_record(env):
# A DANE TLSA record in DNS specifies that connections on a port
# must use TLS and the certificate must match a particular criteria.
#
# Thanks to http://blog.huque.com/2012/10/dnssec-and-certificates.html
# and https://community.letsencrypt.org/t/please-avoid-3-0-1-and-3-0-2-dane-tlsa-records-with-le-certificates/7022
# for explaining all of this! Also see https://tools.ietf.org/html/rfc6698#section-2.1
# and https://github.com/mail-in-a-box/mailinabox/issues/268#issuecomment-167160243.
#
# There are several criteria. We used to use "3 0 1" criteria, which
# meant to pin a leaf (3) certificate (0) with SHA256 hash (1). But
# certificates change, and especially as we move to short-lived certs
# they change often. The TLSA record handily supports the criteria of
# a leaf certificate (3)'s subject public key (1) with SHA256 hash (1).
# The subject public key is the public key portion of the private key
# that generated the CSR that generated the certificate. Since we
# generate a private key once the first time Mail-in-a-Box is set up
# and reuse it for all subsequent certificates, the TLSA record will
# remain valid indefinitely.
from ssl_certificates import load_cert_chain, load_pem
from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat
fn = os.path.join(env["STORAGE_ROOT"], "ssl", "ssl_certificate.pem")
cert = load_pem(load_cert_chain(fn)[0])
subject_public_key = cert.public_key().public_bytes(
Encoding.DER, PublicFormat.SubjectPublicKeyInfo)
# We could have also loaded ssl_private_key.pem and called priv_key.public_key().public_bytes(...)
pk_hash = hashlib.sha256(subject_public_key).hexdigest()
# Specify the TLSA parameters:
# 3: Match the (leaf) certificate. (No CA, no trust path needed.)
# 1: Match its subject public key.
# 1: Use SHA256.
return "3 1 1 " + pk_hash
def build_tlsa_record(env): # A DANE TLSA record in DNS specifies that connections on a port # must use TLS and the certificate must match a particular criteria. # # Thanks to http://blog.huque.com/2012/10/dnssec-and-certificates.html # and https://community.letsencrypt.org/t/please-avoid-3-0-1-and-3-0-2-dane-tlsa-records-with-le-certificates/7022 # for explaining all of this! Also see https://tools.ietf.org/html/rfc6698#section-2.1 # and https://github.com/mail-in-a-box/mailinabox/issues/268#issuecomment-167160243. # # There are several criteria. We used to use "3 0 1" criteria, which # meant to pin a leaf (3) certificate (0) with SHA256 hash (1). But # certificates change, and especially as we move to short-lived certs # they change often. The TLSA record handily supports the criteria of # a leaf certificate (3)'s subject public key (1) with SHA256 hash (1). # The subject public key is the public key portion of the private key # that generated the CSR that generated the certificate. Since we # generate a private key once the first time Mail-in-a-Box is set up # and reuse it for all subsequent certificates, the TLSA record will # remain valid indefinitely. from ssl_certificates import load_cert_chain, load_pem from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat fn = os.path.join(env["STORAGE_ROOT"], "ssl", "ssl_certificate.pem") cert = load_pem(load_cert_chain(fn)[0]) subject_public_key = cert.public_key().public_bytes(Encoding.DER, PublicFormat.SubjectPublicKeyInfo) # We could have also loaded ssl_private_key.pem and called priv_key.public_key().public_bytes(...) pk_hash = hashlib.sha256(subject_public_key).hexdigest() # Specify the TLSA parameters: # 3: Match the (leaf) certificate. (No CA, no trust path needed.) # 1: Match its subject public key. # 1: Use SHA256. return "3 1 1 " + pk_hash
