ASBTutorials/Lab 2 - Certificates/README.md

# 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 <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:

```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
```