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| README.md | ||
Lab 02 - Certificates
Create Working Environment
mkdir -p /root/ca
cd /root/ca
mkdir certs crl newcerts private
chmod 700 private
Create Private Key
openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out private/ca.key.pem
Create Public Key
openssl pkey -in private/ca.key.pem -out ca.key.pem.pub -pubout
Create Certificate Authority
Run using sudo -i:
touch index.txt
echo 1000 > serial
Create OpenSSL config:
vi /root/ca/openssl.cnf
/root/ca/openssl.cnf:
# OpenSSL root CA configuration file.
# Copy to `/root/ca/openssl.cnf`.
[ ca ]
# `man ca`
default_ca = CA_default
[ CA_default ]
# Directory and file locations.
dir = /root/ca
certs = $dir/certs
crl_dir = $dir/crl
new_certs_dir = $dir/newcerts
database = $dir/index.txt
serial = $dir/serial
RANDFILE = $dir/private/.rand
# The root key and root certificate.
private_key = $dir/private/ca.key.pem
certificate = $dir/certs/ca.cert.pem
# For certificate revocation lists.
crlnumber = $dir/crlnumber
crl = $dir/crl/ca.crl.pem
crl_extensions = crl_ext
default_crl_days = 30
# SHA-1 is deprecated, so use SHA-2 instead.
default_md = sha256
name_opt = ca_default
cert_opt = ca_default
default_days = 375
preserve = no
policy = policy_strict
[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
countryName = match
stateOrProvinceName = match
organizationName = match
organizationalUnitName = optional
commonName = supplied
emailAddress = optional
[ policy_loose ]
# Allow the intermediate CA to sign a more diverse range of certificates.
# See the POLICY FORMAT section of the `ca` man page.
countryName = optional
stateOrProvinceName = optional
localityName = optional
organizationName = optional
organizationalUnitName = optional
commonName = supplied
emailAddress = optional
[ req ]
# Options for the `req` tool (`man req`).
default_bits = 2048
distinguished_name = req_distinguished_name
string_mask = utf8only
# SHA-1 is deprecated, so use SHA-2 instead.
default_md = sha256
# Extension to add when the -x509 option is used.
x509_extensions = v3_ca
[ req_distinguished_name ]
# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
countryName = Country Name (2 letter code)
stateOrProvinceName = State or Province Name
localityName = Locality Name
0.organizationName = Organization Name
organizationalUnitName = Organizational Unit Name
commonName = Common Name
emailAddress = Email Address
# Optionally, specify some defaults.
countryName_default = GB
stateOrProvinceName_default = England
localityName_default =
0.organizationName_default = Alice Ltd
organizationalUnitName_default =
emailAddress_default =
[ v3_ca ]
# Extensions for a typical CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, digitalSignature, cRLSign, keyCertSign
[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true, pathlen:0
keyUsage = critical, digitalSignature, cRLSign, keyCertSign
[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = client, email
nsComment = "OpenSSL Generated Client Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection
[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier=keyid:always
[ ocsp ]
# Extension for OCSP signing certificates (`man ocsp`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, digitalSignature
extendedKeyUsage = critical, OCSPSigning
Create root certificate:
openssl req -config openssl.cnf -key private/ca.key.pem -new -x509 -days 7300 -sha256 -extensions v3_ca -out certs/ca.cert.pem
Create Certificate Signing Request
openssl req -new -newkey rsa:2048 -nodes -keyout server.key -out server.csr
Create Certificate Chain
Preparation
mkdir -p /root/intermediate
echo 1000 > /root/intermediate/serial
echo 0100 > /root/intermediate/crlnumber
Configure OpenSSL:
vi /root/intermediate/openssl_intermediate.cnf
openssl_intermediate.cnf:
[ ca ] # The default CA section
default_ca = CA_default # The default CA name
[ CA_default ] # Default settings for the intermediate CA
dir = /root/intermediate # Intermediate CA directory
certs = $dir/certs # Certificates directory
crl_dir = $dir/crl # CRL directory
new_certs_dir = $dir/newcerts # New certificates directory
database = $dir/index.txt # Certificate index file
serial = $dir/serial # Serial number file
RANDFILE = $dir/private/.rand # Random number file
private_key = $dir/private/intermediate.key.pem # Intermediate CA private key
certificate = $dir/certs/intermediate.cert.pem # Intermediate CA certificate
crl = $dir/crl/intermediate.crl.pem # Intermediate CA CRL
crlnumber = $dir/crlnumber # Intermediate CA CRL number
crl_extensions = crl_ext # CRL extensions
default_crl_days = 30 # Default CRL validity days
default_md = sha256 # Default message digest
preserve = no # Preserve existing extensions
email_in_dn = no # Exclude email from the DN
name_opt = ca_default # Formatting options for names
cert_opt = ca_default # Certificate output options
policy = policy_loose # Certificate policy
[ policy_loose ] # Policy for less strict validation
countryName = optional # Country is optional
stateOrProvinceName = optional # State or province is optional
localityName = optional # Locality is optional
organizationName = optional # Organization is optional
organizationalUnitName = optional # Organizational unit is optional
commonName = supplied # Must provide a common name
emailAddress = optional # Email address is optional
[ req ] # Request settings
default_bits = 2048 # Default key size
distinguished_name = req_distinguished_name # Default DN template
string_mask = utf8only # UTF-8 encoding
default_md = sha256 # Default message digest
x509_extensions = v3_intermediate_ca # Extensions for intermediate CA certificate
[ req_distinguished_name ] # Template for the DN in the CSR
countryName = Country Name (2 letter code)
stateOrProvinceName = State or Province Name
localityName = Locality Name
0.organizationName = Organization Name
organizationalUnitName = Organizational Unit Name
commonName = Common Name
emailAddress = Email Address
[ v3_intermediate_ca ] # Intermediate CA certificate extensions
subjectKeyIdentifier = hash # Subject key identifier
authorityKeyIdentifier = keyid:always,issuer # Authority key identifier
basicConstraints = critical, CA:true, pathlen:0 # Basic constraints for a CA
keyUsage = critical, digitalSignature, cRLSign, keyCertSign # Key usage for a CA
[ crl_ext ] # CRL extensions
authorityKeyIdentifier=keyid:always # Authority key identifier
[ server_cert ] # Server certificate extensions
basicConstraints = CA:FALSE # Not a CA certificate
nsCertType = server # Server certificate type
keyUsage = critical, digitalSignature, keyEncipherment # Key usage for a server cert
extendedKeyUsage = serverAuth # Extended key usage for server authentication purposes (e.g., TLS/SSL servers).
authorityKeyIdentifier = keyid,issuer # Authority key identifier linking the certificate to the issuer's public key.
openssl genrsa -out /root/intermediate/intermediate.key.pem 4096
Requesting an Intermediate Certificate
Be sure to specify a fantasy domain name as "Common Name" while generating the request.
cd /root/intermediate
# Create Request
openssl req -new -newkey rsa:2048 -nodes -key intermediate.key.pem -out intermediate.req
Signing the Intermediate Certificate
openssl ca -config /root/ca/openssl.cnf -extensions v3_intermediate_ca -days 3650 -notext -md sha256 -in intermediate.req -out intermediate.cer
You might notice, that - probably due to an error in the lab's paper - signing the certificate is not working.
This is caused by the policy_strict policy which requires the country, city and company of certificate requests to equal with the corresponding fields of the CA's certificate.
Change the CA's policy configuration to policy_loose in order to address the issue:
sed -i 's/^\(policy *= policy_\)strict/\1loose/' /root/ca/openssl.cnf
After that, signing works properly:
openssl ca -config /root/ca/openssl.cnf -extensions v3_intermediate_ca -days 3650 -notext -md sha256 -in intermediate.req -out intermediate.cer
Check the output:
openssl x509 -in intermediate.cer -noout -text
Signing Data
Create a file with secret content:
cd /root
vi secret.txt
Create Signature
# Create and encrypt hash of file
openssl dgst -sha256 -sign /root/ca/private/ca.key.pem -out /tmp/hash.sha256 secret.txt
# Convert hash file to base64
openssl base64 -in /tmp/hash.sha256 -out secret.sig
Verify Signature
Under normal circumstances:
# Re-create hash file from base64
openssl base64 -d -in secret.sig -out /tmp/hash.sha256
# Check integrity of `secret.txt`
openssl dgst -sha256 -verify /root/ca/ca.key.pem.pub -signature /tmp/hash.sha256 secret.txt