# Lab 02 - Certificates ## Create Working Environment ```sh mkdir -p /root/ca cd /root/ca mkdir certs crl newcerts private chmod 700 private ``` ## Create Private Key ```sh openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out private/ca.key.pem ``` ## Create Public Key ```sh openssl pkey -in private/ca.key.pem -out ca.key.pem.pub -pubout ``` ## Create Certificate Authority Run using `sudo -i`: ```sh touch index.txt echo 1000 > serial ``` Create OpenSSL config: ```sh vi /root/ca/openssl.cnf ``` ***`/root/ca/openssl.cnf`:*** ```ini # 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 . 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: ```sh 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 ```sh openssl req -new -newkey rsa:2048 -nodes -keyout server.key -out server.csr ``` ## Create Certificate Chain ### Preparation ```sh mkdir -p /root/intermediate echo 1000 > /root/intermediate/serial echo 0100 > /root/intermediate/crlnumber ``` Configure OpenSSL: ```sh vi /root/intermediate/openssl_intermediate.cnf ``` ***`openssl_intermediate.cnf`:*** ```ini [ 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. ``` ```sh 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. ```sh cd /root/intermediate # Create Request openssl req -new -newkey rsa:2048 -nodes -key intermediate.key.pem -out intermediate.req ``` ### Signing the Intermediate Certificate ```sh 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: ```sh sed -i 's/^\(policy *= policy_\)strict/\1loose/' /root/ca/openssl.cnf ``` After that, signing works properly: ```sh 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: ```sh openssl x509 -in intermediate.cer -noout -text ``` # Signing Data Create a file with secret content: ```sh cd /root vi secret.txt ``` ## Create Signature ```sh # 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: ```sh # 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 ```