Remove key generation (#60)

Closes: https://github.com/scsitape/stenc/issues/3
Closes: https://github.com/scsitape/stenc/issues/32

man/stenc.rst

@@ -8,7 +8,6 @@ stenc - SCSI Tape Hardware Encryption Manager
 SYNOPSIS
 ========
 
-| **stenc** **-g** *length* **-k** *file* [**-kd** *description*]
 | **stenc** **-f** *device* [**--detail**]
 | **stenc** **-f** *device* **-e** **on**\ \|\ **mixed**\ \|\ **rawread** [**-a** *index*] [**-k** *file*] [**--ckod**] [**--protect** \| **--unprotect**]
 | **stenc** **-f** *device* **-e** **off** [**-a** *index*] [**--ckod**] [**--protect** \| **--unprotect**]
@@ -28,29 +27,14 @@ Allows you to manage hardware encryption on SSP enabled tape devices
 OPTIONS
 =======
 
-**-g**\ *length* **-k** **<file to save as>** [**-kd** *<key descriptor(uKAD)>*]
-   Generates a key file of *length* (in bits) containing a random
-   hexadecimal key. After entering this option, you will be required to
-   press random keys followed by the enter key. This will seed the
-   random number generator so that your key is more secure. On systems
-   with **/dev/random**, the key is automatically generated from the
-   random content read from this file. Specify the file to save the key
-   into with the -k option (you will need write permissions to that file
-   location). Lastly you can enter an optional key description using the
-   -kd flag (see *KEY DESCRIPTORS*). This key file can then be used with
-   the **-k** option. You should not generate a key file over an
-   unsecured remote session. Typically, key files should be set to 256
-   bits (32 hexadecimal bytes), however your device may only support 128
-   bits.
-
 **-f** *device*
-   Specifies the device to use (i.e. */dev/nst0, /dev/rmt0.1,
+   Specifies the device to use (i.e. */dev/nst0*, */dev/rmt0.1*,
-   /dev/sg0*). Use the **lsscsi** command to determine the appropriate
+   */dev/sg0*). Use the **lsscsi** command to determine the appropriate
    device to use. You should always use a device name that does not
-   rewind (i.e. use /dev/nst0 instead of /dev/st0, /dev/rmt0.1 instead
+   rewind (i.e. use */dev/nst0* instead of */dev/st0*, */dev/rmt0.1* instead
-   of /dev/rmt0). Use commands like 'cat /proc/scsi/scsi', 'lsscsi', and
+   of */dev/rmt0*). Use commands like 'cat /proc/scsi/scsi', 'lsscsi', and
    'lsdev' to determine the proper device to use. On some distros, a
-   /dev/sg device must be used instead of a /dev/st device.
+   */dev/sg* device must be used instead of a */dev/st* device.
 
    If this is the only option specified, the status of the device will be
    displayed. To retrieve more detailed status information, add
@@ -70,7 +54,7 @@ in order for **stenc** to output the volume status.
 **-e** **on** \| **mixed** \| **rawread** \| **off** 
    Sets the encryption mode for the device specified with **-f** option.
    Successful operations of this type will create an audit entry in the
-   */var/log/stenc* file. If **off** is not specified and the **-k**
+   system log. If **off** is not specified and the **-k**
    option is not specified, the program will require the user to enter a
    hexadecimal key (see *KEY INPUT SYNTAX*) and an optional key
    description (see *KEY DESCRIPTORS*).
@@ -122,68 +106,64 @@ enter the encryption key.
    support these options.
 
 **-k** *file*
-   Only valid when turning encryption on (see the **-e** option) or
+   When turning encryption on, this specifies the location of a key file.
-   generating a new key (see the **-g** option). When turning encryption
-   on, this specifies the location of a key file previously generated
-   with the **-g** option. When generating a new key with the **-g**
-   option, this specifies the key file that the new key will be saved
-   into. Key files should be owned by root ('**chown root**') and only
-   readable by root ('**chmod 600**'). **stenc** automatically chmods
-   key files generated with the **-g** option.
 
 KEY INPUT SYNTAX
 ================
 
-All keys should be a maximum of 256 bits (32 bytes). **stenc** requires that all keys are entered using 2 digit hexadecimal bytes, with no delimiters in between bytes. Do not precede your key input with '0x'. If you try to use a key size that the drive does not support, the command will error. When using a key file, the second line in the file can contain an optional key description that will be displayed with the device status (see the **-f** option).
+**stenc** requires that all keys are entered using 2 digit hexadecimal bytes, with no delimiters in between bytes. Do not precede your key input with '0x'. If you try to use a key size that the drive does not support, the command will error. When using a key file, the second line in the file can contain an optional key description that will be displayed with the device status (see *KEY DESCRIPTORS*).
+
+Keys can be generated using any cryptographically secure entropy source,
+such as the **random**(4) device or the **openssl**(1SSL) suite of commands.
+A 256-bit key file can be created with the following command:
+
+   openssl rand -hex 32
+
+**Example 128 bit key:**
 
-**Example 128 bit Key:**
    000102030405060708090a0b0c0d0e0f
 
-**Example 256 bit Key:**
+**Example 256 bit key:**
+
    000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f
 
+**Example 256 key file with key descriptor:**
+
+   | 000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f
+   | April backup key
+
 EXAMPLE
 =======
 
-**stenc -g 256 -k /etc/tape.key -kd "September Tape Key"** 
+**stenc -f /dev/nst0 -e on -k /etc/stenc.key**
-   Generate a random 256 bit key file with the description "September
+   Turns on encryption on /dev/nst0 using the key contained in
-   Tape Key" and save it into /etc/tape.key
-
-**stenc -f /dev/st0 -e on -k /etc/stenc.key**
-   Turns on encryption on /dev/st0 using the key contained in
    /etc/stenc.key
 
-**stenc -f /dev/st0 -e on**
+**stenc -f /dev/nst0 -e on**
    Asks user to input a key in hexadecimal format and then turns on
-   encryption for /dev/st0 using that key
+   encryption for /dev/nst0 using that key
 
-**stenc -f /dev/st0 -e off**
+**stenc -f /dev/nst0 -e off**
-   Turns off encryption for /dev/st0
+   Turns off encryption for /dev/nst0
 
-**stenc -f /dev/st0 --detail**
+**stenc -f /dev/nst0 --detail**
-   Outputs the detailed encryption status of /dev/st0
+   Outputs the detailed encryption status of /dev/nst0
-
-**tail /var/log/stenc**
-   Lists the last few key change audit entries
 
 KEY CHANGE AUDITING
 ===================
 
 Each time a key is changed using this program, a corresponding entry
-will be entered into the */var/log/stenc* file. These entries will have
+will be entered in the system log. These entries will have
 an *Key Instance Counter* corresponding to the counter listed in the
-device status (see the **-f** option). Each time the key is set, a
+device status (see the **-f** option). Each time the key is set, the
-checksum of that key (or a key description) is also listed in this file.
+key descriptor, if any, is also listed in this file.
 This allows you to know when keys were changed and if the key you are
-using is the same as a prior key. If an unauthorized party would
+using is the same as a prior key.
-compromise this log file, your key security would be decreased if
-checksums were present in the log. To prevent this, you should use key
-descriptors instead of checksums (see *KEY DESCRIPTORS*).
 
 KEY DESCRIPTORS
 ===============
 
-Key descriptors are set when using the **-g** option or the **-e**
+Key descriptors are set when using the **-e**
 option. They will be displayed when retrieving the drive status (see the
 **-f** option). These descriptors will be written to the volume, so they
 should NEVER contain information that would reduce the security of the
@@ -214,5 +194,6 @@ permitted by law.
 SEE ALSO
 ========
 
-| **mt**\ (1L)
+| **openssl**\ (1SSL)
+| **mt**\ (1)
 | **lsscsi**\ (8)

src/main.cpp

@@ -69,7 +69,6 @@ void errorOut(std::string const message);
 void inquiryDrive(std::string tapeDevice);
 void showDriveStatus(std::string tapeDevice, bool detail);
 void showVolumeStatus(std::string tapeDevice);
-std::string randomKey(int length);
 void echo(bool);
 
 static std::optional<std::vector<uint8_t>> key_from_hex_chars(const std::string& s)
@@ -148,21 +147,7 @@ int main(int argc, char **argv) {
       std::cout << "https://github.com/scsitape/stenc \n";
       exit(EXIT_SUCCESS);
     }
-    if (thisCmd == "-g") { // Check if the help flag was passed.  If it was,
+    if (thisCmd == "-e") {
-                           // show usage and exit
-      if (nextCmd == "")
-        errorOut("Key size must be specified when using -g");
-      i++; // skip the next argument
-      keyLength = std::atoi(nextCmd.c_str());
-      if (keyLength % 8 != 0)
-        errorOut("Key size must be divisible by 8");
-      keyLength = keyLength / 8;
-      if (keyLength > SSP_KEY_LENGTH) {
-        std::cout << "Warning: Keys over " << (SSP_KEY_LENGTH * 8)
-                  << " bits cannot be used by this program! \n";
-      }
-      action = 2; // generating key
-    } else if (thisCmd == "-e") {
       if (nextCmd == "")
         errorOut("Key file not specified after -k option");
       if (nextCmd == "on")
@@ -225,25 +210,6 @@ int main(int argc, char **argv) {
     }
   }
 
-  if (action == 2) { // generate key
-    if (keyFile == "") {
-      errorOut("Specify file to save into with the -k argument.");
-    }
-
-    std::string const newkey = randomKey(keyLength);
-    std::ofstream kf{};
-    umask(077); // make sure that no one else can read the new key file
-    kf.open(keyFile.c_str(), std::ios::trunc);
-    if (!kf.is_open()) {
-      errorOut("Could not open '" + keyFile + "' for writing.");
-    }
-    kf << newkey << keyDesc;
-    kf.close();
-    std::cout << "Random key saved into '" << keyFile << "'\n";
-    chmod(keyFile.c_str(), 0600);
-    std::cout << "Permissions of keyfile set to 600\n";
-    exit(EXIT_SUCCESS);
-  }
   // select device from env variable or system default if not given with -f
   if (tapeDrive.empty()) {
     const char *env_tape = getenv("TAPE");
@@ -385,7 +351,7 @@ void errorOut(std::string const message) {
 // shows the command usage
 void showUsage() {
   std::cout
-      << "Usage: stenc --version | -g <length> -k <file> [-kd <description>] | "
+      << "Usage: stenc --version | "
          "-f <device> [--detail] [-e <on/mixed/rawread/off> [-k <file>] "
          "[-kd <description>] [-a <index>] [--protect | --unprotect] [--ckod] ]\n\n"
          "Type 'man stenc' for more information.\n";
@@ -592,38 +558,3 @@ void echo(bool on = true) {
       on ? (settings.c_lflag | ECHO) : (settings.c_lflag & ~(ECHO));
   tcsetattr(STDIN_FILENO, TCSANOW, &settings);
 }
-
-std::string randomKey(int length) {
-  unsigned char rnd;
-  std::stringstream retval{};
-  std::ifstream random{};
-
-  // Under Linux and AIX /dev/random provides much more cryptographically secure
-  // random output than rand()
-  random.open("/dev/random", std::ios::in | std::ios::binary);
-  if (random.is_open()) {
-    for (int i = 0; i < length; i++) {
-      random.read(reinterpret_cast<char *>(&rnd), 1);
-      retval << std::hex << std::setfill('0') << setw(2) << static_cast<int>(rnd);
-    }
-    random.close();
-  } else {
-    std::cout << "Enter random keys on the keyboard to seed the generator.\n"
-                 "End by pressing enter...\n";
-
-    double check = 0;
-    char c = 0;
-    echo(false);
-    while (c != 10) {
-      check += (int)c;
-      c = getchar();
-    }
-    echo(true);
-    srand(time(NULL) + (int)check);
-    for (int i = 0; i < length; i++) {
-      retval << std::hex << (std::rand() % 256);
-    }
-  }
-  retval << std::endl;
-  return (retval.str());
-}