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My knowledge about SSL is very basic and I need to generate self-signed SSL certificates for a local server [server.local] so I can use it in a mobile app for SSL pinning.

How do I create a self-signed certificate, following the rules established by Apple below, via openssl x509?

  • All TLS server certificates must comply with these new security requirements in iOS 13 and macOS 10.15; connections to TLS servers violating these new requirements will fail and may cause network failures, apps to fail, and websites to not load in Safari:
    • Certificates and issuing CAs using RSA keys must use key sizes ≥2048 bits; RSA key sizes <2048 bits are no longer trusted
    • Certificates, and issuing CAs, must use a hash algorithm from the SHA2 family in the signature algorithm; SHA1 signed certificates are no longer trusted for TLS
    • Certificates must present the DNS name of the server in the SubjectAltName extension of the certificate; DNS names in the CommonName of a certificate are no longer trusted
    • Certificates issued after July 1, 2019, as indicated in the NotBefore field of the certificate, must follow these guidelines:
      • Certificates must contain an extendedKeyUsage (EKU) extension containing the id-kp-serverAuth OID
      • Certificates must have a validity period of ≤825 days, as expressed in the NotBefore and NotAfter fields of the certificate.

I created the certificate via:

openssl genrsa -des3 -out myCA.key 2048

openssl req -x509 -new -nodes -key myCA.key -sha256 -days 825 -out myCA.pem

After installing it on the server and device, when I try to use this inside iOS, I get error:

SSL hostname does not match name(s) in certificate,
Extended key usage does not match certificate usage, Root is not trusted`
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Self-signed certificates should never be used, as they have no Chain of Trust and are therefore insecure and pointless; the recommended way is to create a self-signed CA, using that CA to sign the certificate via an openssl.cnf, such as this custom one.

  • The commonName [CN] cannot be an IP or DNS name, since doing so is insecure; I always recommend using the CN to name the cert (e.g. Apache Web Server X, VPN Server 1, etc.)
  • SAN [SubjectAltName] profiles can contain:
    • email: email address
    • URI: Uniform Resource Indicator
    • DNS: DNS domain name [local or FQDN]
    • ID: Registered ID: Object Identifier [OID]
    • IP: IP address
    • dirName: Distinguished Name
    • otherName: OID;content [arbitrary data associated with an OID]
      (Content value is in standard ASN1_generate_nconf format)

Execute all commands from within the directory that will contain openssl.cnf:

  1. Download the custom openssl.cnf: (Linux/Windows) 
    # Linux:
  wget https://raw.githubusercontent.com/JW0914/Wikis/master/Scripts%2BConfigs/OpenSSL/Linux/openssl.cnf

# Windows:
  wget https://raw.githubusercontent.com/JW0914/Wikis/master/Scripts%2BConfigs/OpenSSL/openssl.cnf

  2. Edit the SAN profiles of the certs to be created: (lines 151 - 244)
    1. CA: Edit line 170 [Router.1] to name your CA 
      [ alt_ca_main ]
DNS.1                 = Router.1
IP.1                  = 127.0.0.1
      • [ alt_ca_main ]
        alt_: specifies a SAN profile
        ca_main: custom name for the SAN profile
        (If renaming: update CA V3 profile line 264 [@alt_ca_main])
      • DNS.1:
        Names the CA to make it easier when managing multiple CAs/ICAs
      • IP.1:
        Some router OSes require the loopback IP to be specified in the master CA
    2. Client/Server Cert: Edit lines 189 - 193 
      [ alt_sophos ]
IP.1                = 192.168.2.1
IP.2                = 127.0.0.1
DNS.1               = UTM.WRT
DNS.2               = your.ddns.com
      • [ alt_sophos ]:
        SAN profile name; change sophos only if wishing to rename
        (If renaming: update V3 profile lines 331 [v3_sophos] and 337 [@alt_sophos])
      • IP.1:
        Server IP (if accessible via SSH, loopback IP must be specified [IP.2])
        (list additional IPs on new lines with chronological listings; e.g. IP.3)
      • DNS.1:
        LocalHostname.LocalDomain
      • DNS.2:
        DDNS/FQDN
        (list additional names on new lines with chronological listings; e.g. DNS.3)

  3. Create prerequisite files and directories: (lines 436 - 455) 
    mkdir crl; echo 01 > crl\crlnumber; echo > index; echo > rand; echo 00 > serial
    • crlnumber:
      serial for the next CRL [Certificate Revocation List] signed (lines 443 - 446)
    • index:
      list of all certs created (lines 448 - 451 and 642 - 686)
      • openssl ca must be used to maintain the index automatically, which I don't cover, as it overcomplicates the process (manually maintain: lines 642 - 686)
    • rand:
      random characters used for certificate/key creation (lines 453 - 455)
    • serial:
      serial [hex] of last cert signed, can be any number (lines 438 - 441 and 671 - 681)

  4. Create CA: 
    # CA key should have a secure passphrase of at least 20 characters, containing:
# 2 uppercase, 2 lowercase, 2 numbers, and 2 symbols

  # Request:
    openssl req -x509 -new -sha512 -days 3650 -newkey rsa:4096 -keyout 'CA.key.pem' -out 'CA.crt.pem' -config '.\openssl.cnf' -extensions v3_ca

  # Generate CA CRL Cert:
    openssl ca -gencrl -keyfile 'CA.key.pem' -cert 'CA.crt.pem' -out 'CA.crl.pem' -config '.\openssl.cnf'

  # Convert CA CRL Cert to DER CRL:
    openssl crl -inform PEM -in '.\CA.crl.pem' -outform DER -out '.\CA.crl'
    Most can ignore, as vast majority are fine using RSA:
    Type of key chosen determines the Key Exchange Algorithms that can be used [below]
    • It's imperative the CA V3 profile's KUs are not altered (lines 260 - 265)

  5. (Optional) Create ICA [Intermediate CA]:
    Useful if needing multiple CAs to lower risk of any one being compromised 
    # ICA key should have a secure passphrase of at least 20 characters, containing:
# 2 uppercase, 2 lowercase, 2 numbers, and 2 symbols

  # Request:
    openssl req -out '.\ICA.csr' -new -days 3650 -sha512 -newkey rsa:4096 -keyout 'ICA.key.pem' -config '.\openssl.cnf' -extensions v3_ica_router2

  # Sign ICA with CA:
    openssl x509 -req -sha512 -days 3650 -in '.\ICA.csr' -CA 'CA.crt.pem' -CAkey 'CA.key.pem' -CAserial '.\serial' -out 'ICA.crt.pem' -extfile '.\openssl.cnf' -extensions v3_ica_router2

  # Generate ICA CRL Cert:
    openssl ca -config '.\openssl.cnf' -gencrl -keyfile 'ICA.key.pem' -cert 'ICA.crt.pem' -out '.\ICA.crl.pem'

  # Convert ICA CRL Cert to DER CRL:
    openssl crl -inform PEM -in '.\ICA.crl.pem' -outform DER -out '.\ICA.crl'

  # Concatenate ICA and CA Cert:
    # Linux:
      cat './ICA.crt.pem' './CA.crt.pem' > './CA-ICA-Chain.crt.pem'

    # Windows:
      cmd /c type '.\ICA.crt.pem' '.\CA.crt.pem' > '.\CA-ICA-Chain.crt.pem'
    Most can ignore, as vast majority are fine using RSA:
    Type of key chosen determines the Key Exchange Algorithms that can be used [below]
    • It's imperative the ICA V3 profiles' KUs are not altered (lines 267 - 279)
    • ICA V3 profiles contian pathlen:0 (they can sign certs, but not CAs/ICAs); if pathlen is not specified/number set, it can sign an infinite/specified number of CAs/ICAs

  6. Create certificates: (if V3 profile was renamed in 2.2, update here) 
    # Server certs: add -nodes to the end of the Request command; else server requires
# manually entering encryption passphrase when starting (impractical)

  # Request:
    openssl req -out '.\server.csr' -new -days 825 -sha512 -newkey rsa:2048 -keyout '.\server.key.pem' -config '.\openssl.cnf' -extensions v3_sophos -nodes

  # Sign:
    # CA only:
      openssl x509 -req -sha512 -days 825 -in '.\server.csr' -CA '.\CA.crt.pem' -CAkey '.\CA.key.pem' -CAserial '.\serial' -out '.\server.crt.pem' -extfile '.\openssl.cnf' -extensions v3_sophos

    # ICA: (change to)
      -CA '.\CA-ICA-Chain.crt.pem' -CAkey '.\ICA.key.pem'

  # Chain of Trust: Concatenate CA or ICA and CA to Cert:
    # For ICA, change CA.crt.pem to CA-ICA-Chain.crt.pem

    # Linux:
      cat './CA.crt.pem' >> './server.crt.pem'

    # Windows:
      cmd /c type './CA.crt.pem' >> './server.crt.pem'

  # (Optional) Export:
    # CA only:
      openssl pkcs12 -export -out '.\server.p12' -inkey '.\server.key.pem' -in '.\server.crt.pem' -certfile 'CA.crt.pem'

    # ICA: (change to)
      -certfile 'CA-ICA-Chain.crt.pem'
      # CA - ICA chain cert must be exported to maintain the Chain of Trust of: Cert → ICA → CA
    Most can ignore, as vast majority are fine using RSA:
    Type of key chosen determines the Key Exchange Algorithms that can be used [below]

References:


Certificate Verification:

  • Certificate: 
    openssl x509 -text -noout -in 'cert.crt.pem'
  • Certificate Signing Request [CSR]: 
    openssl req -text -noout -verify -in 'cert.csr'
  • Key: 
    openssl rsa -check -in 'cert.key.pem'
  • PKCS12 [.pfx/.p12]: 
    openssl pkcs12 -info -in 'cert.p12'

Hex ⟷ Dec Conversion:

  • Linux: 
    # hex → dec: (returns 10)
  printf '%d\n' 0x0a

# dec → hex: (returns 0a)
  printf '%x\n' 10
  • Windows:
    Calculator has programmer mode

index:

  • # Manually maintain the index file by inputting one cert entry per line in the following format:

# 1   2----------->   3->   4>  5----->   6---------------------------------------------------------------------------->
  V   261231235959Z         0a  unknown   /C=US/ST=State/L=Locality/O=Org/OU=Unit/CN=Common Name/[email protected]


  # 1 Status of Certificate:
      V                # Valid
      R                # Revoked
      E                # Expired

  # 2 Expiration Date:
      YYMMDDHHMMSSZ    # Date format followed by 'Z' (2026.12.31 @ 23:59:59)

  # 3 Revocation Date: (empty if not revoked)
      YYMMDDHHMMSSZ,reason
      # Valid reasons are:
        ## keyCompromise
        ## CACompromise
        ## affiliationChanged
        ## superseded
        ## cessationOfOperation
        ## certificateHold
        ## privilegeWithdrawn
        ## AACompromise
      # Certain distros error out without a whitespace for 3

  # 4 Serial number in hex format:
      0a               # hex for 10

  # 5 Certificate Filename or Literal String
      unknown          # Certificate filename or literal string 'unknown'

  # 6 Distinguished Name

Key Exchange Algorithms:

  • RSA:
    Encrypts a random value, chosen by the client, via the server public key
    • Required:
      Server public key must be an RSA key
      Server certificate must have KU keyAgreement

  • DH_RSA:
    Key exchange occurs via a static Diffie-Hellman key
    • Required:
      CA must be using an RSA signing key
      Server public key must be a Diffie-Hellman key
      Diffie-Hellman key must have been issued by a CA

  • DH_DSA:
    Like DH_RSA, except the CA used a DSA key in lieu of RSA

  • DHE_RSA:
    Key exchange occurs via an Ephemeral Diffie-Hellman
    • Server dynamically generates & signs a DH public key, sending it to the client
    • Required:
      Server public key must be an RSA key
      Server certificate must have KU digitalSignature

  • DHE_DSA:
    Like DHE_RSA, except the CA used a DSA key in lieu of RSA

Elliptic-Curve Key Exchange Algorithms:

  • ECDH_RSA:
    Like DH_RSA, but with elliptic-curves
    • Required:
      Server public key must be an ECDH key
      Server certificate must be issued by a CA using an RSA public key

  • ECDH_ECDSA:
    Like ECDH_RSA, except the CA used an ECDSA key

  • ECDHE_RSA: Server sends dynamically generated EC Diffie-Hellman key, signing it via it's RSA key
    • Server public key signs the Ephemeral EC Diffie-Hellman key

  • ECDHE_ECDSA:
    Like ECDHE_RSA, except server public key is an ECDSA key
    • Equivalent to DHE_DSS, but with elliptic curves for both the Diffie-Hellman & signature

KUs & EKUs:

Man Pages:

openssl.cnf

While my GitHub will always maintain the customized openssl.cnf linked to throughout, since this answer relies on this, the Linux version is being provided for redundancy:
(Windows version couldn't be included due to the 30K character limit)

#

             ##::[[---  Linux OpenSSL Config  ---]]::##

#====================================================================
                       ##----- Notes -----##
#====================================================================

  # All commands required can be found beginning on line 430

  # Windows users, either:
    # Change file paths from "/" to "\\"
    # Download the Windows openssl.cnf: https://github.com/JW0914/Wikis/blob/master/Scripts+Configs/OpenSSL/openssl.cnf



  # Sophos users:

    # If not using SANs, prior to generating user certs, ensure 'x509_extensions = usr_cert_not_dn'
      # This results with 'RFC822 Name = [email protected]' in the SubjectAlternativeName of the certificate.
        # Without this, it will be impossible to authenticate to VPNs on Sophos.

    # Intermediate CAs & Intermediate CA client certs CANNOT be utilized on Sophos UTM due to how Sophos authenticates.
      # Only exception is the WebAdmin certificate, which can be signed by a Public ICA authority for a FQDN.
        # For chain of trust to be maintained, CA & ICA must be installed on devices accessing the WebAdmin/User Portal.


#====================================================================
             ##----- Establish Build Variables -----##
#====================================================================

dir                             = /etc/ssl
cnf                             = /etc/ssl/openssl.cnf
CNF                             = $dir/openssl.cnf


#====================================================================
           ##----- Establish CA Profile and Policy -----##
#====================================================================

[ default ]
UTM                             = "Sophos UTM CA"
WRT                             = "Router 2 ICA"
VPN                             = "Router 2 VPN ICA"

[ ca ]
default_ca                      = CA_default


#====================================================================

[ CA_default ]
certs                           = $dir
new_certs_dir                   = $dir

database                        = $dir/index
RANDFILE                        = $dir/rand
serial                          = $dir/serial

crldir                          = $dir/crl
crlnumber                       = $crldir/crlnumber
crl                             = $crldir/ca.crl.pem
default_crl_days                = 3650

certificate                     = "$dir/ca/$UTM.crt.pem"
private_key                     = "$dir/ca/$UTM.key.pem"

default_days                    = 3650
preserve                        = no
default_md                      = sha512

x509_extensions                 = usr_cert_not_dn
copy_extensions                 = copy
unique_subject                  = yes

policy                          = policy_match
name_opt                        = esc_2253,esc_ctrl,esc_msb,sep_comma_plus_space,ignore_type
cert_opt                        = ca_default


#====================================================================

[ policy_match ]
countryName                     = match
stateOrProvinceName             = match
organizationName                = match
organizationalUnitName          = match
commonName                      = supplied
emailAddress                    = optional

[ policy_supply ]
countryName                     = match
stateOrProvinceName             = match
organizationName                = match
organizationalUnitName          = match
commonName                      = optional
emailAddress                    = optional


#====================================================================
            ##----- Establish Certificate Options -----#
#--------------------------------------------------------------------

    # x64 machines always process SHA512 faster than SHA256.

    # 'encrypt_key = yes' is not currently commented out.
      # When creating a key for a server, add '-nodes' to the Request command.


[ req ]
default_bits                    = 2048
default_keyfile                 = private.key.pem

preserve                        = no
default_md                      = sha512

string_mask                     = utf8only
utf8                            = yes
distinguished_name              = req_distinguished_name
attributes                      = req_attributes
req_extensions                  = v3_req
x509_extensions                 = v3_ca
copy_extensions                 = copy
encrypt_key                     = yes

[ req_attributes ]
challengePassword               =
challengePassword_min           = 12
challengePassword_max           = 40


#====================================================================

[ req_distinguished_name ]

countryName                     = Country
countryName_max                 = 2
stateOrProvinceName             = State
localityName                    = Locality
0.organizationName              = Organization
organizationalUnitName          = Organizational Unit
commonName                      = Common Name
commonName_max                  = 64
emailAddres                     = Email
emailAddress_max                = 64

countryName_default             = xx
stateOrProvinceName_default     = State
localityName_default            = Locality
0.organizationName_default      = Sophos UTM
organizationalUnitName_default  = LAN


#====================================================================
      ##----- Establish SubjectAltName (SAN) Profiles -----##
#====================================================================

  # All server certs with WebUIs should have their loopback IP specified in their SAN profile.
    # This prevents certificate errors if connecting to the device, router, or server via an SSH tunnel.
      # Certain OS CA certs must have the loopback IP specified in SAN profile (i.e. Sophos UTM's CA).

  # Provided SAN profiles are utilized, Common Names can be whatever one wishes (i.e. not the DNS or IP)
    # SANs can be: 'email' (email address), 'URI' (Uniform Resource Indicator), 'DNS' (DNS domain name),
    # 'RID' (Registered ID: OBJECT IDENTIFIER), 'IP' (IP address), 'dirName' (Distinguished Name), and 'otherName'.


#--------------------------------------------------------------------
               ##----- Certificate Authorities -----##
#--------------------------------------------------------------------

# Main #
  [ alt_ca_main ]
  DNS.1                 = Router.1
  IP.1                  = 127.0.0.1

# Router 2 #
  [ alt_ica_router2 ]
  DNS.1                 = Router.2
  IP.1                  = 127.0.0.1

# Code Signing #
  [ alt_signing_ica ]
  DNS.1                 = Code-Signing

#--------------------------------------------------------------------
            ##----- Certificate Authority Clients -----##
#--------------------------------------------------------------------

# Main #

  # Servers #
    [ alt_sophos ]
    IP.1                = 192.168.2.1
    IP.2                = 127.0.0.1
    DNS.1               = UTM.WRT
    DNS.2               = your.ddns.com

    [ alt_truenas ]
    IP.1                = 192.168.2.13
    IP.2                = 192.168.2.130
    IP.3                = 127.0.0.1
    DNS.1               = TrueNAS.WRT
    DNS.2               = your-fqdn.com

    [ alt_vpn_server1 ]
    IP.1                = 10.0.0.1
    DNS.1               = your.ddns.com

  # Clients #
    [ alt_vpn1_user1 ]
    email.1             = [email protected]
    DNS.1               = VPN1-Client1-Device1
    DNS.2               = VPN1-Client1-Device2


#--------------------------------------------------------------------
     ##----- Intermediate Certificate Authority Clients -----##
#--------------------------------------------------------------------

# Router 2 #

  # Servers #
    [ alt_openwrt ]
    IP.1                = 192.168.2.2
    IP.2                = 127.0.0.1
    DNS.1               = LAN.WRT

    [ alt_vpn_server2 ]
    IP.1                = 10.0.1.1
    DNS.1               = your.ddns.com

  # Clients #
    [ alt_vpn2_user1 ]
    DNS.1               = VPN2-Client1-Device1
    email.1             = [email protected]

    [ alt_vpn2_user2 ]
    DNS.1               = VPN2-Client2-Device1
    DNS.2               = VPN2-Client2-Device2
    email.1             = [email protected]


# Code Signing #

  # Cert1 #
    [ alt_codesign ]
    email.1             = [email protected]


#====================================================================
     ##----- Establish Certificate Authority V3 Profiles -----##
#--------------------------------------------------------------------

  # These V3 CA profiles must not be modified to contain any more, or any less, KUs.

  # These have been configured specifically for security & its imperative no other keyUsages are set
    # For an ICA to be capable of signing CAs/ICAs, 'pathlen' number must mirror number of CAs/ICAs it can sign

  # By default, all ICAs 'pathlen' values are set to 0, meaning they can sign certs, but not other CAs/ICAs.
    # If 'pathlen' is not specified, CA/ICA can sign an infinite number of other CAs/ICAs.


[ v3_ca ]
basicConstraints            = critical, CA:TRUE
subjectKeyIdentifier        = hash
authorityKeyIdentifier      = keyid:always, issuer:always
subjectAltName              = @alt_ca_main
keyUsage                    = critical, cRLSign, digitalSignature, keyCertSign

[ v3_ica_router2 ]
basicConstraints            = critical, CA:TRUE, pathlen:0
subjectKeyIdentifier        = hash
authorityKeyIdentifier      = keyid:always, issuer:always
subjectAltName              = @alt_ica_router2
keyUsage                    = critical, cRLSign, digitalSignature, keyCertSign

[ v3_signing_ica ]
basicConstraints            = critical, CA:TRUE, pathlen:0
subjectKeyIdentifier        = hash
authorityKeyIdentifier      = keyid:always, issuer:always
keyUsage                    = critical, cRLSign, digitalSignature, keyCertSign
subjectAltName              = @alt_signing_ica

[ crl_ext ]
issuerAltName               = issuer:copy
authorityKeyIdentifier      = keyid:always, issuer:always


#====================================================================
    ##----- Establish Generalized V3 Certificate Profiles -----##
#--------------------------------------------------------------------

[ v3_req ]
basicConstraints            = critical, CA:FALSE
subjectKeyIdentifier        = hash

[ usr_cert_dn ]
basicConstraints            = critical, CA:FALSE
subjectKeyIdentifier        = hash
authorityKeyIdentifier      = keyid:always, issuer:always
keyUsage                    = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage            = critical, clientAuth, emailProtection

[ usr_cert_not_dn ]
basicConstraints            = critical, CA:FALSE
subjectKeyIdentifier        = hash
authorityKeyIdentifier      = keyid:always, issuer:always
subjectAltName              = email:copy
keyUsage                    = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage            = critical, clientAuth, emailProtection


#====================================================================
      ##----- Establish Client Certificate V3 Profiles -----##
#--------------------------------------------------------------------

  # These V3 profiles should not be modified to contain less than what they are currently configured with.
    # These have been specifically configured with security in mind.

  # All servers capable of TLS should contain all keyUsages, except for 'dataEncipherment'
    # VPN and file servers should not have less than: 'digitalSignature, keyEncipherment, keyAgreement'

  # All servers must contain EKU 'serverAuth'
    # All server [VPN] clients must contain EKU 'clientAuth'


#--------------------------------------------------------------------
            ##----- Certificate Authority Clients -----##
#--------------------------------------------------------------------

# Main #

  # Servers #
    [ v3_sophos ]
    basicConstraints            = critical, CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment, keyAgreement
    extendedKeyUsage            = critical, serverAuth
    subjectAltName              = @alt_sophos

    [ v3_truenas ]
    basicConstraints            = critical, CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment, keyAgreement
    extendedKeyUsage            = critical, serverAuth
    subjectAltName              = @alt_truenas

    [ v3_vpn_server1 ]
    basicConstraints            = critical, CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment, keyAgreement
    extendedKeyUsage            = critical, serverAuth
    subjectAltName              = @alt_vpn_server1

  # Clients #
    [ v3_vpn1_user1 ]
    basicConstraints            = critical,CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment
    extendedKeyUsage            = critical, clientAuth
    subjectAltName              = @alt_vpn1_user1


#--------------------------------------------------------------------
      ##----- Intermediate Certificate Authority Clients -----##
#--------------------------------------------------------------------

# Router 2 #

  # Servers #
    [ v3_openwrt ]
    basicConstraints            = critical, CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment, keyAgreement
    extendedKeyUsage            = critical, serverAuth
    subjectAltName              = @alt_openwrt

    [ v3_vpn_server2 ]
    basicConstraints            = critical, CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment, keyAgreement
    extendedKeyUsage            = critical, serverAuth
    subjectAltName              = @alt_vpn_server2

  # Clients #
    [ v3_vpn2_user1 ]
    basicConstraints            = critical,CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment
    extendedKeyUsage            = critical, clientAuth
    subjectAltName              = @alt_vpn2_user1

    [ v3_vpn2_user2 ]
    basicConstraints            = critical,CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, digitalSignature, keyEncipherment
    extendedKeyUsage            = critical, clientAuth
    subjectAltName              = @alt_vpn2_user2


# Code Signing #

  # Certificates #
    [ v3_codesign ]
    basicConstraints            = critical, CA:FALSE
    subjectKeyIdentifier        = hash
    authorityKeyIdentifier      = keyid:always, issuer:always
    keyUsage                    = critical, nonRepudiation, digitalSignature
    extendedKeyUsage            = critical, codeSigning, msCodeInd, msCodeCom, msCTLSign, timeStamping
    subjectAltName              = @alt_codesign
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  • 1
    “Self-signed certificates should never be used, as they have no Chain of Trust and are therefore insecure and pointless” – This is simply not correct. There is no difference in security or trust whatsoever. Especially considering how OP wants to use this certificate with pinning.
    – Daniel B
    Commented Jan 16, 2021 at 17:27
  • @DanielB It only leaves the user wide open to a MITM attack... If it's worth doing, it worth doing right the first time. I know very little about SSL Pinning, but this article does a decent job at detailing how a self-signed cert leaves every client at risk of a MITM attack due to the inherent lack of a Chain of Trust. Considering it takes all of ~2min to issue a self-signed CA for signing the server cert, why would anyone logically not do so? The goal is to increase security, not open ourselves up to be exploited by a MITM.
    – JW0914
    Commented Jan 16, 2021 at 17:56
  • Except it doesn’t. Trust is all the same, whether it’s chained from a CA or directly applied to a specific certificate. A full PKI offers some benefits, especially with replacing certificates, but it doesn’t offer any improvement regarding trust or MITM.
    – Daniel B
    Commented Jan 16, 2021 at 21:31
  • @DanielB would you please provide a more in-depth explanation, or link to a reference that offers a more in-depth explanation, as I couldn't find any search result that recommended a self-signed cert for SSL pinning? Also, from the error the OP received [Root is not trusted], if using a self-signed cert it would need to be installed as a Root CA to comply, which isn't recommended in general and implies improper Chain of Trust.
    – JW0914
    Commented Jan 20, 2021 at 12:35
  • 1
    A self-signed certificate does not offer advantages. It is merely equivalent. I don’t have any reference on that. OP is actually receiving three error messages, one of which is the one you quote. // Again: Using self-signed certificates or CAs does not imply a trust issue. You just need to make sure you trust the right thing. Using established trusted channels to distribute certificates is advisable.
    – Daniel B
    Commented Jan 20, 2021 at 13:44

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