nervuri 2 years ago
commit 2547e348b8


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# Generate CA + wildcard cert for any hostname
CA_name='local CA'
./ <host> Generate a CA and sign a wildacrd cert for <host> with it.'
set -o errexit # (-e) exit immediately if any command has a non-zero exit status
set -o nounset # (-u) don't accept undefined variables
#set -o xtrace # for debugging
# Check input.
if [ "$#" -lt 1 ] || [ "$#" -gt 1 ]; then
>&2 echo "$helptext"
exit 1
# Check if host is an IP address.
# If `ipcalc-ng` is available, use it.
if command -v ipcalc-ng >/dev/null; then
if ipcalc-ng -sc "$host"; then
# Else if `ip` is available, use it.
# Note: a simple number also passes this check,
# but it's good enough for our purposes.
elif command -v ip >/dev/null; then
if ip route get "$host" >/dev/null 2>&1; then
# If host is an IDN, convert it to punycode.
# Use the `idn` command, if available.
if command -v idn >/dev/null; then
host=$(echo "$host" | idn)
# Create CA directory, if it does not exist.
mkdir -p CA
cd CA
# Generate CA.
if [ ! -f "ca.key" ] && [ ! -f "ca.crt" ]; then
openssl genrsa -out ca.key 2048
openssl req -new -x509 -key ca.key -out ca.crt -subj "/CN=$CA_name" -days 30
openssl x509 -in ca.crt -noout -text
# Copy the CA cert under a new name, allowing it to be accepted in the
# Android trust store (/system/etc/security/cacerts/).
mkdir -p android
filename=$(openssl x509 -inform PEM -subject_hash_old -in ca.crt | head -1)
cp ca.crt "android/$filename.0"
# Generate wildcard cert.
if [ ! -f "$host.key" ] && [ ! -f "$host.crt" ]; then
# Set the Subject Alternative Name based on whether
# the host is an IP address or not.
if [ $ip -eq 1 ]; then
SAN2="IP = $host"
SAN1="DNS:*.$host, DNS:$host"
SAN2="DNS.1 = *.$host
DNS.2 = $host"
openssl genrsa -out "$host.key" 2048
openssl req -new -key "$host.key" -out "$host.csr" -subj "/CN=$host" \
-addext "subjectAltName = $SAN1"
#openssl req -in "$host.csr" -noout -text
# Prepare X.509 extensions file.
echo "basicConstraints=CA:FALSE
subjectKeyIdentifier = hash
[ my_subject_alt_names ]
$SAN2" > ext.conf
# Sign the cert.
openssl x509 -req -in "$host.csr" -out "$host.crt" -days 30 \
-CA ca.crt -CAkey ca.key -extfile ext.conf -CAcreateserial
openssl x509 -in "$host.crt" -noout -text
rm "$host.csr"
# Remove X.509 extensions file.
rm ext.conf
# Create bundle (probably not be required).
#cat "$host.crt" ca.crt > "$host.bundle.crt"
# Show generated files.
if command -v tree >/dev/null; then
cd ..
echo '=== Generated files ==='
tree CA

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## Generate CA + wildcard cert for any hostname
`` takes a domain name as input and outputs a directory named "CA", containing:
- a certificate authority (private key + cert + serial number file + a copy of the cert appropriately named for inclusion in the Android trust store);
- a CA-signed cert for the provided hostname;
- if the hostname is a domain, then a wildcard cert is generated, matching `domain.tld` and `*.domain.tld`;
- the hostname can also be an IP address.
Both the CA and the cert are valid for 30 days.
## Usage
## Optional dependencies
- `ipcalc-ng`, for detecting if the supplied hostname is an IP address.
- `idn`, for converting [IDNs]( to punycode.
## Adding the CA to the Android trust store
The reason I wrote this script was to intercept an Android app's TLS-encrypted traffic. In order to do this, the CA cert must be added to the Android trust store. Here's how:
In Android versions prior to 4, see
In Android versions 4, 5 and 6, you can simply copy the file to your phone and add it from the Android UI.
In Android 7+, in order for the CA to be trusted by all apps, you need to have a rooted phone. Allow USB debugging, grant root access for ADB, connect the phone to a computer and run the following commands:
# restart ADB as root
adb root
# remount the /system partition as read+write
adb remount
# copy the CA file to the root store
adb push CA/android/*.0 /system/etc/security/cacerts/
Then you can spoof a domain's IP address by adding it to the Android system's hosts file:
adb shell 'echo "" >> /system/etc/hosts'
To allow TLS interception on a non-rooted phone, you need to slightly modify the app you are snooping on, as described in:
If the app uses certificate pinning, you may need a program like [Apktool](, [Frida]( or [baksmali](
Thanks to Soarez for his [OpenSSL CA guide](!