Ok, we found the solution (many thanks to @Bernie_O ): the post by “fixitnowyes” on Apple-discussions gives the necessary instructions to create a certificate which will be accepted by my iOS 13 devices! I am quite happy to have syncing reminders on my local server again.
Don’t foget to import the new certificate to the iOS device and switch on the “trust” (settings / general / about / scroll down to “certificate trust settings”).
Edit: This is the content of the above-mentioned post or - if german-speaking - read a Blog-Artikel darüber :
Create a file “server-selfsigned-CA.cnf” with content (replace your.servers.domain.com with domain name of server and 10.0.0.1 with IP of your server):
[ req ]
default_bits = 4096
default_keyfile = server-selfsigned-CA.key
default_md = sha256
default_days = 824
encrypt_key = no
distinguished_name = subject
req_extensions = req_ext
x509_extensions = x509_ext
string_mask = utf8only
prompt = no
# The Subject DN can be formed using X501 or RFC 4514 (see RFC 4519 for a description).
# Its sort of a mashup. For example, RFC 4514 does not provide emailAddress.
[ subject ]
OU = Company Inc.
countryName = DE
stateOrProvinceName = Berlin
localityName = Berlin
organizationName = Company Inc.
# Use a friendly name here because it's presented to the user. The server's DNS
# names are placed in Subject Alternate Names. Plus, DNS names here is deprecated
# by both IETF and CA/Browser Forums. If you place a DNS name here, then you
# must include the DNS name in the SAN too (otherwise, Chrome and others that
# strictly follow the CA/Browser Baseline Requirements will fail).
commonName = aFriendlyName
emailAddress = some@mail.com
# Section x509_ext is used when generating a self-signed certificate. I.e., openssl req -x509 ...
[ x509_ext ]
subjectKeyIdentifier = hash
#authorityKeyIdentifier = keyid,issuer
authorityKeyIdentifier = keyid:always,issuer
# You only need digitalSignature below. *If* you don't allow
# RSA Key transport (i.e., you use ephemeral cipher suites), then
# omit keyEncipherment because that's key transport.
basicConstraints = critical, CA:TRUE
keyUsage = critical, digitalSignature, keyEncipherment, cRLSign, keyCertSign
subjectAltName = DNS:your.servers.domain.com, DNS:10.0.0.1
# nsComment = "OpenSSL Generated Certificate"
extendedKeyUsage = serverAuth
# RFC 5280, Section 4.2.1.12 makes EKU optional
# CA/Browser Baseline Requirements, Appendix (B)(3)(G) makes me confused
# In either case, you probably only need serverAuth.
# extendedKeyUsage = serverAuth, clientAuth
extendedKeyUsage = TLS Web Server Authentication
# Section req_ext is used when generating a certificate signing request. I.e., openssl req ...
[ req_ext ]
subjectKeyIdentifier = hash
basicConstraints = CA:FALSE
keyUsage = digitalSignature, keyEncipherment
subjectAltName = DNS:your.servers.domain.com, DNS:10.0.0.1
nsComment = "OpenSSL Generated Certificate"
# RFC 5280, Section 4.2.1.12 makes EKU optional
# CA/Browser Baseline Requirements, Appendix (B)(3)(G) makes me confused
# In either case, you probably only need serverAuth.
#extendedKeyUsage = serverAuth, clientAuth
# [ alternate_names ]
# DNS.1 = example.com
# DNS.2 = www.example.com
# DNS.3 = mail.example.com
# DNS.4 = ftp.example.com
# Add these if you need them. But usually you don't want them or
# need them in production. You may need them for development.
# DNS.5 = localhost
# DNS.6 = localhost.localdomain
# DNS.7 = 127.0.0.1
Generate a new certificate using the .cnf file:
sudo openssl req -config server-selfsigned-CA.cnf -new -x509 -out server-selfsigned-CA.crt -days 825
You can check if the certificate was created correctly with:
openssl x509 -in server-selfsigned-CA.crt -text -noout
Import the file “server-selfsigned-CA.crt” to iOS device (I used a SMB connection and the new “files”-app).
On the iOS device, go to settings and install the certificate.
Then, go to settings / general / about / scroll down to “certificate trust settings” and switch on trust for the certificate.
And that’s it, reminders app will sync again.