Sign SSL Certificate by Your Own CA with x509 extension

Following is introducing three layers SSL certificate chain

For adding x509 extension in certificate, a configuration files should be used rather than just type an option in command when you sign a certificate.

This topic introduces how to generate a SSL certificate chain with X509 extension.

A. Root as CA Sign an Intermediate Certificate

A.1. Generate Self-sign Certificate to pretend a root CA and private key.

a. Command to generate self-signed CA root certificate and private key

=>rootMediumMainCert.pem, rootMediumMainKey.pem

# openssl req -x509 -days 3650 -newkey rsa:2048 -keyout rootMediumMainKey.pem -out rootMediumMainCert.pem

b. Check the certificate

# openssl x509 -in rootMediumMainCert.pem -text
Certificate:
 Data:
 Version: 3 (0x2)
 Serial Number:
 d0:c1:93:56:ca:46:1f:d5
 Signature Algorithm: sha256WithRSAEncryption
 Issuer: C=CN, ST=Hong KOng, L=Kwun Tong, O=MediumMain, OU=Publisher, CN=www.medium_main.tk
 Validity
 Not Before: Jul 25 09:54:55 2018 GMT
 Not After : Jul 22 09:54:55 2028 GMT
 Subject: C=CN, ST=Hong KOng, L=Kwun Tong, O=MediumMain, OU=Publisher, CN=www.medium_main.tk
 Subject Public Key Info:
 Public Key Algorithm: rsaEncryption
 Public-Key: (2048 bit)
 Modulus:
 00:d3:49:1f:42:5a:d7:7e:84:eb:2f:ae:79:2c:69:
 b2:2f:d2:b1:83:81:56:43:4d:ad:21:e7:a9:a7:ab:
 ce:d2:5a:a8:aa:ea:3d:d5:8d:7b:e1:9e:19:1a:32:
 f3:c9:31:00:fd:ac:f4:71:b4:38:7e:4c:5b:63:72:
 ca:9d:dd:4d:8d:65:b0:44:f8:00:1c:ad:84:25:f6:
 30:aa:67:84:4e:cf:26:c4:98:5f:1f:1b:4c:64:a5:
 4b:dc:a3:16:1d:f1:03:65:e8:e4:0a:33:61:fb:ed:
 da:24:75:c8:15:b7:55:d4:2c:3f:99:6f:3f:30:87:
 84:33:c7:d3:2f:af:37:bd:88:ee:4c:35:6d:6b:2d:
 6a:49:14:0d:ea:40:c4:07:eb:95:3b:e9:12:a7:3a:
 19:b5:04:1b:1b:89:3f:ba:c7:9f:52:1a:36:78:55:
 6f:85:94:c4:7d:e0:28:d2:41:27:6b:86:fe:c4:58:
 d2:66:6b:35:4b:f5:ef:a9:72:f6:c0:5c:fb:b1:98:
 50:0b:da:42:60:75:08:5f:15:c5:56:38:23:64:49:
 4c:8e:75:af:8c:2d:35:7f:fa:68:9e:cd:91:84:cd:
 0b:3d:e7:53:71:64:26:b7:94:92:56:77:1e:79:dd:
 04:a1:c5:8f:05:70:8d:bd:45:04:1d:03:18:a0:3d:
 ce:31
 Exponent: 65537 (0x10001)
 X509v3 extensions:
 X509v3 Subject Key Identifier:
 07:8C:C1:29:24:98:D6:6B:0E:DA:05:3F:13:4E:30:FB:E0:39:EB:B0
 X509v3 Authority Key Identifier:
 keyid:07:8C:C1:29:24:98:D6:6B:0E:DA:05:3F:13:4E:30:FB:E0:39:EB:B0
X509v3 Basic Constraints:
 CA:TRUE

2. Create Intermediate Certificate Request File

a. Prepare a configuration file for intermediate CSR file

=>intMediumPressCsr.conf

#This section is named req because the command we are using is req
# (openssl req …)
[ req ]
# This specifies the default key size in bits. If not specified then 512 is
# used. It is used if the -new option is used. It can be overridden by using
# the -newkey option. 
default_bits = 2048
# This is the default filename to write a private key to. If not specified the
# key is written to standard output. This can be overridden by the -keyout
# option.
default_keyfile = intMediumPressKey.pem
# If this is set to no then if a private key is generated it is not encrypted.
# This is equivalent to the -nodes command line option. For compatibility
# encrypt_rsa_key is an equivalent option. 
encrypt_key = no
# This option specifies the digest algorithm to use. Possible values include
# md5 sha1 mdc2. If not present then MD5 is used. This option can be overridden
# on the command line.
default_md = sha256
# if set to the value no this disables prompting of certificate fields and just
# takes values from the config file directly. It also changes the expected
# format of the distinguished_name and attributes sections.
prompt = no
# if set to the value yes then field values to be interpreted as UTF8 strings,
# by default they are interpreted as ASCII. This means that the field values,
# whether prompted from a terminal or obtained from a configuration file, must
# be valid UTF8 strings.
utf8 = yes
# This specifies the section containing the distinguished name fields to
# prompt for when generating a certificate or certificate request.
distinguished_name = my_req_distinguished_name
# this specifies the configuration file section containing a list of extensions
# to add to the certificate request. It can be overridden by the -reqexts
# command line switch. See the x509v3_config(5) manual page for details of the
# extension section format.
req_extensions = my_extensions
[my_req_distinguished_name]
C = CN
ST = Hong Kong
L = Kwun Tong
O = MediumPress
OU = Press
CN = www.medium_press.tk
[my_extensions]
basicConstraints=CA:TRUE
extendedKeyUsage = serverAuth, clientAuth, codeSigning, emailProtection
keyUsage = nonRepudiation, digitalSignature, keyEncipherment

b. Command to generate intermediate CSR file

=> intMediumPressCert.csr

# openssl req -new -out intMediumPressCert.csr -config intMediumPressCsr.conf

The private key file has been generated at the same time, this is based on the configuration parameter,

default_keyfile = intMediumPressKey.pem in configuration file.

3. Sign the intermediate certificate by root

a. Prepare extension configuration file for intermediate certificate

=>intMediumPressExt.conf

basicConstraints=CA:TRUE
subjectKeyIdentifier = hash

b. Prepare ca configuration file for root CA certificate

=>rootMediumMainCa.conf

# ‘ca’ as the default section because we’re usign the ca command
# we use ‘ca’ as the default section because we’re usign the ca command
[ ca ]
default_ca = ca_sign
[ ca_sign ]
# a text file containing the next serial number to use in hex. Mandatory.
# This file must be present and contain a valid serial number.
serial = ./intMediumPress.srl
# the text database file to use. Mandatory. This file must be present though
# initially it will be empty.
database = ./inter_index.txt
# specifies the directory where new certificates will be placed. Mandatory.
new_certs_dir = ./intermediateCert
# the file containing the CA certificate. Mandatory
certificate = ./rootMediumMainCert.pem
# the file contaning the CA private key. Mandatory
private_key = ./rootMediumMainKey.pem
# the message digest algorithm. Remember to not use MD5
default_md = sha256
# for how many days will the signed certificate be valid
default_days = 1000
# a section with a set of variables corresponding to DN fields
policy = my_policy
[ my_policy ]
# if the value is “match” then the field value must match the same field in the
# CA certificate. If the value is “supplied” then it must be present.
# Optional means it may be present. Any fields not mentioned are silently
# deleted.
countryName = match
stateOrProvinceName = supplied
organizationName = supplied
commonName = supplied
organizationalUnitName = optional
commonName = supplied

c. Create a subdirectory (same as setting in rootMediumMainCa.conf) for placing output certificate temporary

# mkdir intermediateCert

d. Create text database file (same as setting in rootMediumMainCa.conf)

# touch inter_index.txt

e. Create serial number for output certificate by random number, the output serial number file is same as setting in rootMediumMainCa.conf

# echo $(od -vAn -N8 -tx8 < /dev/random) > intMediumPress.srl

f. Command to sign certificate

# openssl ca -config rootMediumMainCa.conf -out intMediumPressCert.pem -extfile intMediumPressExt.conf -in intMediumPressCert.csr

g. Check the certificate

# openssl x509 -in intMediumPressCert.pem -text
Certificate:
Data:
Version: 3 (0x2)
Serial Number: 8407366217844970047 (0x74acf707ef44d23f)
Signature Algorithm: sha256WithRSAEncryption
Issuer: C=CN, ST=Hong KOng, L=Kwun Tong, O=MediumMain, OU=Publisher, CN=www.medium_main.tk
Validity
Not Before: Jul 26 02:43:40 2018 GMT
Not After : Apr 21 02:43:40 2021 GMT
Subject: C=CN, ST=Hong Kong, O=MediumPress, OU=Press, CN=www.medium_press.tk
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
Public-Key: (2048 bit)
Modulus:
00:df:77:59:11:d3:b6:da:01:1f:64:69:18:18:a0:
ba:11:da:b3:ef:55:4e:7c:4c:92:43:b7:73:20:83:
9c:34:86:ed:ce:df:b8:a5:09:7e:88:51:68:08:21:
b9:e6:e6:1e:33:99:07:bb:9f:be:96:24:7c:1c:27:
92:3f:16:c5:e8:a8:46:26:56:4f:2e:ac:a5:69:48:
cd:37:03:d2:4d:87:75:ce:53:34:94:86:f6:cd:8b:
a5:f7:0f:c2:ec:70:b3:d7:78:5d:2f:21:de:61:87:
72:8e:c5:57:ad:be:f6:92:93:ec:db:77:1a:30:6f:
4b:9b:77:7b:0f:98:77:05:3f:7a:da:7b:e1:59:57:
54:65:65:68:26:86:7d:22:90:91:e4:b1:4a:b1:c0:
c9:ce:c6:45:e0:96:94:46:6d:c4:3f:84:ae:85:e0:
4a:42:ac:c3:83:7d:da:c5:b3:a7:a4:c0:e6:6e:45:
8d:55:b8:4c:b4:11:01:01:cc:a5:5b:92:d7:a2:16:
3e:61:d9:38:f0:46:5b:9d:2e:d2:ad:a9:cc:57:e3:
2e:8f:92:c4:15:65:53:35:46:d2:8b:3f:ef:8f:55:
87:ac:ed:ea:e2:a5:5d:c9:9b:e8:f9:14:a6:7a:72:
06:57:14:11:ce:36:3b:8d:59:20:d7:9f:b0:0d:24:
91:19
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Basic Constraints:
CA:TRUE
X509v3 Subject Key Identifier:
9B:9F:CC:D0:E8:53:B0:45:CA:4A:D8:44:56:62:80:B2:F7:22:AD:B8

B. Intermediate Certificate Sign a Server

We have already done a intermediate certificate signed by own CA root certificate, now let cascade the procedure to sign a certificate chain to produce server certificate eventually.

1. Create Server Certificate Request File

a. Prepare a configuration file for server CSR file

=>serverLunarMythosCsr.conf

#This section is named req because the command we are using is req
# (openssl req …)
[ req ]
# This specifies the default key size in bits. If not specified then 512 is
# used. It is used if the -new option is used. It can be overridden by using
# the -newkey option.
default_bits = 2048
# This is the default filename to write a private key to. If not specified the
# key is written to standard output. This can be overridden by the -keyout
# option.
default_keyfile = serverLunarMythosKey.pem
# If this is set to no then if a private key is generated it is not encrypted.
# This is equivalent to the -nodes command line option. For compatibility
# encrypt_rsa_key is an equivalent option.
encrypt_key = yes
# This option specifies the digest algorithm to use. Possible values include
# md5 sha1 mdc2. If not present then MD5 is used. This option can be overridden
# on the command line.
default_md = sha256
# if set to the value no this disables prompting of certificate fields and just
# takes values from the config file directly. It also changes the expected
# format of the distinguished_name and attributes sections.
prompt = no
# if set to the value yes then field values to be interpreted as UTF8 strings,
# by default they are interpreted as ASCII. This means that the field values,
# whether prompted from a terminal or obtained from a configuration file, must
# be valid UTF8 strings.
utf8 = yes
# This specifies the section containing the distinguished name fields to
# prompt for when generating a certificate or certificate request.
distinguished_name = my_req_distinguished_name
# this specifies the configuration file section containing a list of extensions
# to add to the certificate request. It can be overridden by the -reqexts
# command line switch. See the x509v3_config(5) manual page for details of the
# extension section format.
req_extensions = my_extensions
[my_req_distinguished_name]
C = CN
ST = Hong Kong
L = Kwun Tong
O = Lunar Mythos
OU = Press
CN = www.lunarmythos.tk
[my_extensions]
basicConstraints=CA:TRUE
extendedKeyUsage = serverAuth, clientAuth, codeSigning, emailProtection
keyUsage = nonRepudiation, digitalSignature, keyEncipherment

b. Generate Server Certificate Sign Request File based on configuration file in step a.

=>serverLunarMythosCert.csr

# openssl req -new -out serverLunarMythosCert.csr -config serverLunarMythosCsr.conf

2. Sign a server certificate by intermediate

a. Prepare extension configuration file for server certificate

=>serverLunarMythosExt.conf

basicConstraints=CA:TRUE
subjectKeyIdentifier = hash

b. Prepare CA configuration file for intermediate certificate as CA

=>intMediumPressCa.conf

#’ca’ as the default section because we’re usign the ca command
# we use ‘ca’ as the default section because we’re usign the ca command
[ ca ]
default_ca = ca_sign
[ ca_sign ]
# a text file containing the next serial number to use in hex. Mandatory.
# This file must be present and contain a valid serial number.
serial = ./serverLunarMythos.srl
# the text database file to use. Mandatory. This file must be present though
# initially it will be empty.
database = ./server_index.txt
# specifies the directory where new certificates will be placed. Mandatory.
new_certs_dir = ./serverCert
# the file containing the CA certificate. Mandatory
certificate = ./intMediumPressCert.pem
# the file contaning the CA private key. Mandatory
private_key = ./ intMediumPressKey.pem
# the message digest algorithm. Remember to not use MD5
default_md = sha256
# for how many days will the signed certificate be valid
default_days = 365
# a section with a set of variables corresponding to DN fields
policy = my_policy
[ my_policy ]
# if the value is “match” then the field value must match the same field in the
# CA certificate. If the value is “supplied” then it must be present.
# Optional means it may be present. Any fields not mentioned are silently
# deleted.
countryName = match
stateOrProvinceName = supplied
organizationName = supplied
commonName = supplied
organizationalUnitName = optional
commonName = supplied

b. Create a subdirectory (consistent to setting in rootMediumMainCa.conf) for placing output server certificate temporary.

# mkdir serverCert

b. Create text database file (consistent to setting in rootMediumMainCa.conf)

# touch server_index.txt

c. Create serial number file for output certificate by random number. (File name should be consistent to setting in rootMediumMainCa.conf

# echo $(od -vAn -N8 -tx8 < /dev/random) > serverLunaryMythos.srl

d. Command to sign certificate

# openssl ca -config intMediumPressCa.conf -out serverLunarMythosCert.pem -extfile serverLunarMythosExt.conf -in serverLunarMythosCert.csr

e. Check the final server certificate

# openssl x509 -in serverLunarMythosCert.pem -text
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
f0:d6:cb:dd:46:37:fb:c0
Signature Algorithm: sha256WithRSAEncryption
Issuer: C=CN, ST=Hong Kong, O=MediumPress, OU=Press, CN=www.medium_press.tk
Validity
Not Before: Jul 26 03:32:12 2018 GMT
Not After : Jul 26 03:32:12 2019 GMT
Subject: C=CN, ST=Hong Kong, O=Lunar Mythos, OU=Press, CN=www.lunarmythos.tk
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
Public-Key: (2048 bit)
Modulus:
00:ad:1d:0e:b3:76:1e:57:eb:fc:60:b8:3c:d0:0d:
aa:25:e9:b0:01:d8:8d:c3:2a:45:04:1d:8c:38:fc:
10:c4:b8:96:95:6b:6f:0e:73:72:8d:04:38:72:72:
7f:fe:9a:78:4b:30:86:96:81:00:5a:ef:75:b8:e8:
bd:04:92:cd:c0:92:69:33:45:26:b3:9f:48:a7:4b:
02:09:a8:cd:57:a7:b8:e1:2b:a2:01:28:ec:dd:6b:
e3:17:5e:f8:e9:31:b5:48:46:a0:6c:7c:f6:f8:fe:
ac:b5:04:c1:9b:d1:d9:56:9d:3d:10:be:41:3a:9a:
5b:11:8a:a5:3a:4c:31:5c:d5:ca:7e:2c:28:c1:b3:
bf:5b:28:97:59:a3:5b:c4:05:24:d7:93:16:74:7a:
1d:e6:4e:f8:e9:af:54:0f:d8:8f:2d:60:07:d6:4c:
70:b4:38:73:3e:16:7c:d3:cb:29:c4:81:bd:c5:cb:
ff:4e:b5:2e:a3:bb:7d:a8:39:bc:47:cd:4c:58:74:
3c:cc:a9:2a:43:5a:0f:09:e2:e3:35:a1:23:63:90:
85:57:82:d2:d5:07:d9:ee:41:80:db:94:8c:37:f5:
e2:b2:4b:ae:c9:4f:d6:c7:b9:14:1b:f1:0f:b2:6c:
7d:ae:c9:21:e9:a2:3a:f4:cd:91:db:85:5d:4b:a7:
08:af
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Basic Constraints:
CA:TRUE
X509v3 Subject Key Identifier:
B9:C8:8D:41:D1:03:83:3A:38:BE:0F:30:08:60:45:AE:88:BE:06:01

C. Final Verification of Certificate Chain

openssl verify -CAfile rootMediumMainCert.pem -untrusted intMediumPressCert.pem serverLunarMythosCert.pem
serverLunarMythosCert.pem: OK

— END —