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Protecting Your SSH Keys With SmartCard-HSM

I use a yubi key for my ssh authentication. But I’ve other ssh keys for my remote services so wanted something that allows me to take a backup of my keys see this post for more information on to backup/restore a SmartCard-HSM

Create your first ssh keypair

Verify your smartcard connection

Insert you smartcard and verify the connection, see my previous post if you need more information about the smartcard initialization

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[staf@vicky ~]$ pkcs11-tool -L
Available slots:
Slot 0 (0xffffffffffffffff): Virtual hotplug slot
  (empty)
Slot 1 (0x1): Generic Smart Card Reader Interface [Smart Card Reader Interface
  token label        : SmartCard-HSM (UserPIN)
  token manufacturer : www.CardContact.de
  token model        : PKCS#15 emulated
  token flags        : rng, login required, PIN initialized, token initialized
  hardware version   : 24.13
  firmware version   : 1.2
  serial num         : DECM0102331
[staf@vicky ~]$ 

Create your keypair

Create your ssh key pair and give the a meaningful label

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[staf@vicky ~]$ pkcs11-tool --slot 1 --keypairgen --key-type rsa:2048 --label my_ssh_key --login
Logging in to "SmartCard-HSM (UserPIN)".
Please enter User PIN: 
Key pair generated:
Private Key Object; RSA 
  label:      my_ssh_key
  ID:         fca6240eeef8d3156f0c4dfc591b2d938d6104cb
  Usage:      decrypt, sign, unwrap
Public Key Object; RSA 2048 bits
  label:      my_ssh_key
  ID:         fca6240eeef8d3156f0c4dfc591b2d938d6104cb
  Usage:      encrypt, verify, wrap
[staf@vicky ~]$ 

Extract your public key

We used PKCS11 to generate the keypair, PKCS15 is designed identify users to applications.

Dump the token content

Dump the token content to get the id of your ssh keypair.

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[staf@vicky ~]$ pkcs15-tool -D
Using reader with a card: Generic Smart Card Reader Interface [Smart Card Reader Interface] (20070818000000000) 00 00
PKCS#15 Card [SmartCard-HSM]:
        Version        : 0
        Serial number  : DECM0102331
        Manufacturer ID: www.CardContact.de
        Flags          : 

PIN [UserPIN]
        Object Flags   : [0x3], private, modifiable
        ID             : 01
        Flags          : [0x81A], local, unblock-disabled, initialized, exchangeRefData
        Length         : min_len:6, max_len:15, stored_len:0
        Pad char       : 0x00
        Reference      : 129 (0x81)
        Type           : ascii-numeric
        Tries left     : 3

PIN [SOPIN]
        Object Flags   : [0x1], private
        ID             : 02
        Flags          : [0x9E], local, change-disabled, unblock-disabled, initialized, soPin
        Length         : min_len:16, max_len:16, stored_len:0
        Pad char       : 0x00
        Reference      : 136 (0x88)
        Type           : bcd
        Tries left     : 3

Private EC Key [myfirst_keypair]
        Object Flags   : [0x3], private, modifiable
        Usage          : [0x10C], sign, signRecover, derive
        Access Flags   : [0x1D], sensitive, alwaysSensitive, neverExtract, local
        FieldLength    : 256
        Key ref        : 1 (0x1)
        Native         : yes
        Path           : e82b0601040181c31f0201::
        Auth ID        : 01
        ID             : ae79417e809ed19b9a69d4c14f444462ad0bd66c
        MD:guid        : {efac9b29-2289-658c-98d1-af5af965d484}
          :cmap flags  : 0x0
          :sign        : 0
          :key-exchange: 0

Private RSA Key [my_ssh_key]
        Object Flags   : [0x3], private, modifiable
        Usage          : [0x2E], decrypt, sign, signRecover, unwrap
        Access Flags   : [0x1D], sensitive, alwaysSensitive, neverExtract, local
        ModLength      : 2048
        Key ref        : 2 (0x2)
        Native         : yes
        Path           : e82b0601040181c31f0201::
        Auth ID        : 01
        ID             : fca6240eeef8d3156f0c4dfc591b2d938d6104cb
        MD:guid        : {a272b2ad-ff6f-606c-801a-4153be498018}
          :cmap flags  : 0x0
          :sign        : 0
          :key-exchange: 0

Public EC Key [myfirst_keypair]
        Object Flags   : [0x0]
        Usage          : [0x0]
        Access Flags   : [0x2], extract
        FieldLength    : 256
        Key ref        : 0 (0x0)
        Native         : no
        ID             : ae79417e809ed19b9a69d4c14f444462ad0bd66c
        DirectValue    : <present>

Public RSA Key [my_ssh_key]
        Object Flags   : [0x0]
        Usage          : [0x0]
        Access Flags   : [0x2], extract
        ModLength      : 2048
        Key ref        : 0 (0x0)
        Native         : no
        ID             : fca6240eeef8d3156f0c4dfc591b2d938d6104cb
        DirectValue    : <present>

[staf@vicky ~]$ 

Get the public key

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[staf@vicky ~]$ pkcs15-tool --read-ssh-key fca6240eeef8d3156f0c4dfc591b2d938d6104cb
Using reader with a card: Generic Smart Card Reader Interface [Smart Card Reader Interface] (20070818000000000) 00 00
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCWShfPjqh+pU8lCoIhXIXh+cGpSem1iNFH6TuluQQLPiqPIeObCTfqC8q9TjR/2FYzG+3ECdiRr0fiywE9OnzUgJI5oOjXfMwY3xE1PbYBrSvYERofhkEv2ejlyRifN3sbLGSU0V7pX+BNOuiJCquCehPMV9+ehkjbk9hPRFUzL1GywsOkmWUoIzrdjH0dlhPX3TUCdoizWAIdUqg+RX4DCEc52RvaGdX4Tn2THxeffXqFJ/gKkParZSLmOND1iRhtJeJ8CmgAqfD8ReshbcSs231h/QvUl3JaThcrLbPrSQFzVUH+rN+pGlSl722NWyPNPWlwwE+SreTLbQRoWayN my_ssh_key
[staf@vicky ~]$ 

Configure the remote host

Add the key to the remote host

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staf@vicky .ssh]$ vi authorized_keys 
[staf@vicky .ssh]$ 

Test the connection

Test you ssh connection with the PKCS11 interface:

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[staf@vicky ~]$ ssh localhost
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).

With the PKCS11 interface enabled:

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[staf@vicky ~]$ ssh -o "PKCS11Provider opensc-pkcs11.so" localhost
C_GetAttributeValue failed: 18
Enter PIN for 'SmartCard-HSM (UserPIN)': 
Last login: Thu Dec  3 09:55:23 2015 from ::1
gpg-agent[17327]: enabled debug flags: command cache ipc
gpg-agent: a gpg-agent is already running - not starting a new one
gpg-agent: secmem usage: 0/32768 bytes in 0 blocks
[staf@vicky ~]$ 

Update your ssh_config

Add PKCS11Provider opensc-pkcs11.so to your ~/.ssh/config or your global ssh_config

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staf@vicky ~]$ cd .ssh/
[staf@vicky .ssh]$ vim config
PKCS11Provider opensc-pkcs11.so
[staf@vicky .ssh]$ 

Have fun …