Protecting Files With the Solaris Cryptographic Framework

This section describes how to generate symmetric keys, how to create checksums for file integrity, and how to protect files from eavesdropping. The commands in this section can be run by regular users. Developers can write scripts that use these commands.

How to Generate a Symmetric Key by Using the dd Command

A key is needed to encrypt files and to generate the MAC of a file. The key should be derived from a random pool of numbers.

If your site has a random number generator, use the generator. Otherwise, you can use the dd command with the Solaris /dev/urandom device as input. For more information, see the dd(1M) man page.

1. Determine the key length that your algorithm requires.

   1. List the available algorithms.

      % encrypt -l Algorithm Keysize: Min Max (bits) ------------------------------------------ aes 128 128 arcfour 8 128 des 64 64 3des 192 192 % mac -l Algorithm Keysize: Min Max (bits) ------------------------------------------ des_mac 64 64 sha1_hmac 8 512 md5_hmac 8 512 sha256_hmac 8 512 sha384_hmac 8 1024 sha512_hmac 8 1024

   2. Determine the key length in bytes to pass to the dd command.

      Divide the minimum and maximum key sizes by 8. When the minimum and maximum key sizes are different, intermediate key sizes are possible. For example, the value 8, 16, or 64 can be passed to the dd command for the sha1_hmac and md5_hmac functions.

2. Generate the symmetric key.

   % dd if=/dev/urandom of=keyfile bs=n count=n

   if=file

   Is the input file. For a random key, use the /dev/urandom file.

   of=keyfile

   Is the output file that holds the generated key.

   bs=n

   Is the key size in bytes. For the length in bytes, divide the key length in bits by 8.

   count=n

   Is the count of the input blocks. The number for n should be 1.

3. Store your key in a protected directory.

   The key file should not be readable by anyone but the user.

   % chmod 400 keyfile

Example 14–1 Creating a Key for the AES Algorithm

In the following example, a secret key for the AES algorithm is created. The key is also stored for later decryption. AES mechanisms use a 128-bit key. The key is expressed as 16 bytes in the dd command.

% ls -al ~/keyf
drwx------   2 jdoe  staff        512 May 3 11:32 ./
% dd if=/dev/urandom of=$HOME/keyf/05.07.aes16 bs=16  count=1
% chmod 400 ~/keyf/05.07.aes16

Example 14–2 Creating a Key for the DES Algorithm

In the following example, a secret key for the DES algorithm is created. The key is also stored for later decryption. DES mechanisms use a 64-bit key. The key is expressed as 8 bytes in the dd command.

% dd if=/dev/urandom of=$HOME/keyf/05.07.des8 bs=8  count=1
% chmod 400 ~/keyf/05.07.des8

Example 14–3 Creating a Key for the 3DES Algorithm

In the following example, a secret key for the 3DES algorithm is created. The key is also stored for later decryption. 3DES mechanisms use a 192-bit key. The key is expressed as 24 bytes in the dd command.

% dd if=/dev/urandom of=$HOME/keyf/05.07.3des.24 bs=24 count=1
% chmod 400 ~/keyf/05.07.3des.24

Example 14–4 Creating a Key for the MD5 Algorithm

In the following example, a secret key for the MD5 algorithm is created. The key is also stored for later decryption. The key is expressed as 64 bytes in the dd command.

% dd if=/dev/urandom of=$HOME/keyf/05.07.mack64 bs=64 count=1
% chmod 400 ~/keyf/05.07.mack64

How to Generate a Symmetric Key by Using the pktool Command

Some applications require a symmetric key for encryption and decryption of communications. In this procedure, you create a symmetric key and store it.

• If your site has a random number generator, you can use the generator to create a random number for the key. This procedure does not use your site's random number generator.

• You can instead use the dd command with the Solaris /dev/urandom device as input. The dd command does not store the key. For the procedure, see How to Generate a Symmetric Key by Using the dd Command.

1. (Optional) If you plan to use a keystore, create it.

   • To create and initialize a PKCS #11 keystore, see How to Generate a Passphrase by Using the pktool setpin Command.

   • To create and initialize an NSS database, see Example 15–5.

2. Generate a random number for use as a symmetric key.

   Use one of the following methods.

   • Generate a key and store it in a file.

     The advantage of a file-stored key is that you can extract the key from this file for use in an application's key file, such as the /etc/inet/secret/ipseckeys file or IPsec.

     % pktool genkey keystore=file outkey=key-fn \ [keytype=specific-symmetric-algorithm] [keylen=size-in-bits] \ [dir=directory] [print=n]

     keystore

     The value file specifies the file type of storage location for the key.

     outkey=key-fn

     Is the filename when keystore=file.

     keytype=specific-symmetric-algorithm

     For a particular algorithm, specify aes, arcfour, des, or 3des.

     keylen=size-in-bits

     Is the length of the key in bits. The number must be divisible by 8. Do not specify for des or 3des.

     dir=directory

     Is the directory path to key-fn. By default, directory is the current directory.

     print=n

     Prints the key to the terminal window. By default, the value of print is n.

   • Generate a key and store it in a PKCS #11 keystore.

     The advantage of the PKCS #11 keystore is that you can retrieve the key by its label. This method is useful for keys that encrypt and decrypt files. You must complete Step 1 before using this method.

     % pktool genkey label=key-label \ [keytype=specific-symmetric-algorithm] [keylen=size-in-bits] \ [token=token] [sensitive=n] [extractable=y] [print=n]

     label=key-label

     Is a user-specified label for the key. The key can be retrieved from the keystore by its label.

     keytype=specific-symmetric-algorithm

     For a particular algorithm, specify aes, arcfour, des, or 3des.

     keylen=size-in-bits

     Is the length of the key in bits. The number must be divisible by 8. Do not specify for des or 3des.

     token=token

     Is the token name. By default, the token is Sun Software PKCS#11 softtoken.

     sensitive=n

     Specifies the sensitivity of the key. When the value is y, the key cannot be printed by using the print=y argument. By default, the value of sensitive is n.

     extractable=y

     Specifies that the key can be extracted from the keystore. Specify n to prevent the key from being extracted.

     print=n

     Prints the key to the terminal window. By default, the value of print is n.

   • Generate a key and store it in an NSS keystore.

     You must complete Step 1 before using this method.

     % pktool keystore=nss genkey label=key-label \ [keytype=[keytype=specific-symmetric-algorithm] [keylen=size-in-bits] [token=token] \ [dir=directory-path] [prefix=database-prefix]

     keystore

     The value nss specifies the NSS type of storage location for the key.

     label=key-label

     Is a user-specified label for the key. The key can be retrieved from the keystore by its label.

     keytype=specific-symmetric-algorithm

     For a particular algorithm, specify aes, arcfour, des, or 3des.

     keylen=size-in-bits

     Is the length of the key in bits. The number must be divisible by 8. Do not specify for des or 3des.

     token=token

     Is the token name. By default, the token is the NSS internal token.

     dir=directory

     Is the directory path to the NSS database. By default, directory is the current directory.

     prefix=directory

     Is the prefix to the NSS database. The default is no prefix.

     print=n

     Prints the key to the terminal window. By default, the value of print is n.

3. (Optional) Verify that the key exists.

   Use one of the following commands, depending on where you stored the key.

   • Verify the key in the key-fn file.

     % pktool list keystore=file objtype=key infile=key-fn Found n keys. Key #1 - keytype:location (keylen)

   • Verify the key in the PKCS #11 or the NSS keystore.

     $ pktool list objtype=key Enter PIN for keystore: Found n keys. Key #1 - keytype:location (keylen)

Example 14–5 Creating a DES Key by Using the pktool Command

In the following example, a secret key for the DES algorithm is created. The key is stored in a local file for later decryption. The command protects the file with 400 permissions. When the key is created, the print=y option displays the generated key in the terminal window.

DES mechanisms use a 64-bit key. The user who owns the keyfile retrieves the key by using the od command.

% pktool genkey keystore=file outkey=64bit.file1 keytype=des print=y
        Key Value ="a3237b2c0a8ff9b3"
% od -x 64bit.file1
0000000 a323 7b2c 0a8f f9b3

How to Compute a Digest of a File

When you compute a digest of a file, you can check to see that the file has not been tampered with by comparing digest outputs. A digest does not alter the original file.

1. List the available digest algorithms.

   % digest -l md5 sha1 sha256 sha384 sha512

2. Compute the digest of the file and save the digest listing.

   Provide an algorithm with the digest command.

   % digest -v -a algorithm input-file > digest-listing

   -v

   Displays the output in the following format:

   algorithm (input-file) = digest

   -a algorithm

   Is the algorithm to use to compute a digest of the file. Type the algorithm as the algorithm appears in the output of Step 1.

   input-file

   Is the input file for the digest command.

   digest-listing

   Is the output file for the digest command.

Example 14–6 Computing a Digest With the MD5 Mechanism

In the following example, the digest command uses the MD5 mechanism to compute a digest for an email attachment.

% digest -v -a md5 email.attach >>  $HOME/digest.emails.05.07
% cat  ~/digest.emails.05.07
md5 (email.attach) = 85c0a53d1a5cc71ea34d9ee7b1b28b01

When the -v option is not used, the digest is saved with no accompanying information:

% digest -a md5 email.attach >>  $HOME/digest.emails.05.07
% cat  ~/digest.emails.05.07
85c0a53d1a5cc71ea34d9ee7b1b28b01

Example 14–7 Computing a Digest With the SHA1 Mechanism

In the following example, the digest command uses the SHA1 mechanism to provide a directory listing. The results are placed in a file.

% digest -v -a sha1 docs/* > $HOME/digest.docs.legal.05.07
% more ~/digest.docs.legal.05.07
sha1 (docs/legal1) = 1df50e8ad219e34f0b911e097b7b588e31f9b435
sha1 (docs/legal2) = 68efa5a636291bde8f33e046eb33508c94842c38
sha1 (docs/legal3) = 085d991238d61bd0cfa2946c183be8e32cccf6c9
sha1 (docs/legal4) = f3085eae7e2c8d008816564fdf28027d10e1d983

How to Compute a MAC of a File

A message authentication code, or MAC, computes a digest for the file and uses a secret key to further protect the digest. A MAC does not alter the original file.

1. List the available mechanisms.

   % mac -l Algorithm Keysize: Min Max ----------------------------------- des_mac 64 64 sha1_hmac 8 512 md5_hmac 8 512 sha256_hmac 8 512 sha384_hmac 8 1024 sha512_hmac 8 1024

2. Generate a symmetric key of the appropriate length.

   You have two options. You can provide a passphrase from which a key will be generated. Or you can provide a key.

   • If you provide a passphrase, you must store or remember the passphrase. If you store the passphrase online, the passphrase file should be readable only by you.

   • If you provide a key, it must be the correct size for the mechanism. For the procedure, see How to Generate a Symmetric Key by Using the dd Command.

3. Create a MAC for a file.

   Provide a key and use a symmetric key algorithm with the mac command.

   % mac -v -a algorithm [ -k keyfile ] input-file

   -v

   Displays the output in the following format:

   algorithm (input-file) = mac

   -a algorithm

   Is the algorithm to use to compute the MAC. Type the algorithm as the algorithm appears in the output of the mac -l command.

   -k keyfile

   Is the file that contains a key of algorithm-specified length.

   input-file

   Is the input file for the MAC.

Example 14–8 Computing a MAC With DES_MAC and a Passphrase

In the following example, the email attachment is authenticated with the DES_MAC mechanism and a key that is derived from a passphrase. The MAC listing is saved to a file. If the passphrase is stored in a file, the file should not be readable by anyone but the user.

% mac -v -a des_mac email.attach
Enter passphrase: <Type passphrase>
des_mac (email.attach) = dd27870a
% echo "des_mac (email.attach) = dd27870a" >> ~/desmac.daily.05.07

Example 14–9 Computing a MAC With MD5_HMAC and a Key File

In the following example, the email attachment is authenticated with the MD5_HMAC mechanism and a secret key. The MAC listing is saved to a file.

% mac -v -a md5_hmac -k $HOME/keyf/05.07.mack64 email.attach
md5_hmac (email.attach) = 02df6eb6c123ff25d78877eb1d55710c
% echo "md5_hmac (email.attach) = 02df6eb6c123ff25d78877eb1d55710c" \
>> ~/mac.daily.05.07

Example 14–10 Computing a MAC With SHA1_HMAC and a Key File

In the following example, the directory manifest is authenticated with the SHA1_HMAC mechanism and a secret key. The results are placed in a file.

% mac -v -a sha1_hmac \
-k $HOME/keyf/05.07.mack64 docs/* > $HOME/mac.docs.legal.05.07
% more ~/mac.docs.legal.05.07
sha1_hmac (docs/legal1) = 9b31536d3b3c0c6b25d653418db8e765e17fe07a
sha1_hmac (docs/legal2) = 865af61a3002f8a457462a428cdb1a88c1b51ff5
sha1_hmac (docs/legal3) = 076c944cb2528536c9aebd3b9fbe367e07b61dc7
sha1_hmac (docs/legal4) = 7aede27602ef6e4454748cbd3821e0152e45beb4

How to Encrypt and Decrypt a File

When you encrypt a file, the original file is not removed or changed. The output file is encrypted.

For solutions to common errors from the encrypt command, see the section that follows the examples.

1. Create a symmetric key of the appropriate length.

   You have two options. You can provide a passphrase from which a key will be generated. Or you can provide a key.

   • If you provide a passphrase, you must store or remember the passphrase. If you store the passphrase online, the passphrase file should be readable only by you.

   • If you provide a key, it must be the correct size for the mechanism. For the procedure, see How to Generate a Symmetric Key by Using the dd Command.

2. Encrypt a file.

   Provide a key and use a symmetric key algorithm with the encrypt command.

   % encrypt -a algorithm [ -k keyfile ] -i input-file -o output-file

   -a algorithm

   Is the algorithm to use to encrypt the file. Type the algorithm as the algorithm appears in the output of the encrypt -l command.

   -k keyfile

   Is the file that contains a key of algorithm-specified length. The key length for each algorithm is listed, in bits, in the output of the encrypt -l command.

   -i input-file

   Is the input file that you want to encrypt. This file is left unchanged by the command.

   -o output-file

   Is the output file that is the encrypted form of the input file.

Example 14–11 Encrypting and Decrypting With AES and a Passphrase

In the following example, a file is encrypted with the AES algorithm. The key is generated from the passphrase. If the passphrase is stored in a file, the file should not be readable by anyone but the user.

% encrypt -a aes -i ticket.to.ride -o ~/enc/e.ticket.to.ride
Enter passphrase: <Type passphrase>
Re-enter passphrase: Type passphrase again

The input file, ticket.to.ride, still exists in its original form.

To decrypt the output file, the user uses the same passphrase and encryption mechanism that encrypted the file.

% decrypt -a aes -i ~/enc/e.ticket.to.ride -o ~/d.ticket.to.ride
Enter passphrase: <Type passphrase>

Example 14–12 Encrypting and Decrypting With AES and a Key File

In the following example, a file is encrypted with the AES algorithm. AES mechanisms use a key of 128 bits, or 16 bytes.

% encrypt -a aes -k ~/keyf/05.07.aes16 \
-i ticket.to.ride -o ~/enc/e.ticket.to.ride 

The input file, ticket.to.ride, still exists in its original form.

To decrypt the output file, the user uses the same key and encryption mechanism that encrypted the file.

% decrypt -a aes -k ~/keyf/05.07.aes16  \
-i ~/enc/e.ticket.to.ride -o ~/d.ticket.to.ride

Example 14–13 Encrypting and Decrypting With ARCFOUR and a Key File

In the following example, a file is encrypted with the ARCFOUR algorithm. The ARCFOUR algorithm accepts a key of 8 bits (1 byte), 64 bits (8 bytes), or 128 bits (16 bytes).

% encrypt -a arcfour -i personal.txt \
-k ~/keyf/05.07.rc4.8 -o ~/enc/e.personal.txt

To decrypt the output file, the user uses the same key and encryption mechanism that encrypted the file.

% decrypt -a arcfour -i ~/enc/e.personal.txt \
-k ~/keyf/05.07.rc4.8 -o ~/personal.txt

Example 14–14 Encrypting and Decrypting With 3DES and a Key File

In the following example, a file is encrypted with the 3DES algorithm. The 3DES algorithm requires a key of 192 bits, or 24 bytes.

% encrypt -a 3des -k ~/keyf/05.07.des24 \
-i ~/personal2.txt -o ~/enc/e.personal2.txt

To decrypt the output file, the user uses the same key and encryption mechanism that encrypted the file.

% decrypt -a 3des -k ~/keyf/05.07.des24 \
-i ~/enc/e.personal2.txt -o ~/personal2.txt

Troubleshooting

The following messages indicate that the key that you provided to the encrypt command is not permitted by the algorithm that you are using.

• encrypt: unable to create key for crypto operation: CKR_ATTRIBUTE_VALUE_INVALID

• encrypt: failed to initialize crypto operation: CKR_KEY_SIZE_RANGE

If you pass a key that does not meet the requirements of the algorithm, you must supply a better key.

• One option is to use a passphrase. The framework then provides a key that meets the requirements.

• The second option is to pass a key size that the algorithm accepts. For example, the DES algorithm requires a key of 64 bits. The 3DES algorithm requires a key of 192 bits.