btrbk: add openssl_enc encryption for raw targets; add system_urandom()

Example:

Manually create a key:

    # KEYFILE=/some/secure/place/btrbk.key
    # dd if=/dev/urandom bs=1 count=32 | od -x -A n | tr -d "[:space:]" > $KEYFILE

btrbk.conf:

    volume /mnt/btr_pool
      incremental no
      raw_target_encrypt  openssl_enc
      openssl_ciphername  aes-256-cbc
      openssl_iv_size     16  # NOTE: set to "no" if no IV is needed by the selected cipher
      openssl_keyfile     /some/secure/place/btrbk.key

      subvolume home
        target raw ssh://cloud.example.com/backup

ChangeLog

@@ -9,6 +9,7 @@ btrbk-current
   * Add "--preserve-snapshots" and "--preserve-backups" options.
   * Change raw backup format (sidecar file instead of uuid in file).
   * Honor target_preserve for raw targets (delete raw targets).
+  * Add symmetric encryption for raw targets (close #157).
   * Do not run in "perl taint mode" by default: remove "perl -T" in
     hashbang; hardcode $PATH only if taint mode is enabled.
   * Remove "duration" column from transaction_log/transaction_syslog.

btrbk

@@ -62,7 +62,7 @@ my $glob_match = qr/[0-9a-zA-Z_@\+\-\.\/\*]+/;  # file_match plus '*'
 my $uuid_match = qr/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}/;
 my $timestamp_postfix_match = qr/\.(?<YYYY>[0-9]{4})(?<MM>[0-9]{2})(?<DD>[0-9]{2})(T(?<hh>[0-9]{2})(?<mm>[0-9]{2})((?<ss>[0-9]{2})(?<zz>(Z|[+-][0-9]{4})))?)?(_(?<NN>[0-9]+))?/;  # matches "YYYYMMDD[Thhmm[ss+0000]][_NN]"
 my $raw_postfix_match_DEPRECATED = qr/--(?<received_uuid>$uuid_match)(\@(?<parent_uuid>$uuid_match))?\.btrfs?(\.(?<compress>($compress_format_alt)))?(\.(?<encrypt>gpg))?(\.(?<split>split))?(\.(?<incomplete>part))?/;  # matches ".btrfs_<received_uuid>[@<parent_uuid>][.gz|bz2|xz][.gpg][.split][.part]"
-my $raw_postfix_match = qr/\.btrfs(\.($compress_format_alt))?(\.gpg)?/;  # matches ".btrfs[.gz|bz2|xz][.gpg]"
+my $raw_postfix_match = qr/\.btrfs(\.($compress_format_alt))?(\.(gpg|encrypted))?/;  # matches ".btrfs[.gz|bz2|xz][.gpg|encrypted]"
 
 my $group_match = qr/[a-zA-Z0-9_:-]+/;
 my $ssh_cipher_match = qr/[a-z0-9][a-z0-9@.-]+/;
@@ -105,11 +105,14 @@ my %config_options = (
   raw_target_compress         => { default => undef,     accept => [ "no", (keys %compression) ] },
   raw_target_compress_level   => { default => "default", accept => [ "default" ], accept_numeric => 1 },
   raw_target_compress_threads => { default => "default", accept => [ "default" ], accept_numeric => 1 },
-  raw_target_encrypt          => { default => undef,     accept => [ "no", "gpg" ] },
+  raw_target_encrypt          => { default => undef,     accept => [ "no", "gpg", "openssl_enc" ] },
   raw_target_block_size       => { default => "128K",    accept_regexp => qr/^[0-9]+(kB|k|K|KiB|MB|M|MiB)?$/ },
   raw_target_split            => { default => undef,     accept => [ "no" ], accept_regexp => qr/^[0-9]+([kmgtpezyKMGTPEZY][bB]?)?$/ },
   gpg_keyring                 => { default => undef,     accept_file => { absolute => 1 } },
   gpg_recipient               => { default => undef,     accept_regexp => qr/^[0-9a-zA-Z_@\+\-\.]+$/ },
+  openssl_ciphername          => { default => "aes-256-cbc", accept_regexp => qr/^[0-9a-zA-Z\-]+$/ },
+  openssl_iv_size             => { default => undef,     accept => [ "no", accept_numeric => 1 ] },
+  openssl_keyfile             => { default => undef,     accept_file => { absolute => 1 } },
 
   group                       => { default => undef,     accept_regexp => qr/^$group_match(\s*,\s*$group_match)*$/, split => qr/\s*,\s*/ },
 
@@ -231,6 +234,8 @@ my %raw_info_sort = (
   compress             => 9,
   split                => 10,
   encrypt              => 11,
+  cipher               => 12,
+  iv                   => 13,
  );
 
 my %url_cache;       # map URL to btr_tree node
@@ -1379,6 +1384,14 @@ sub btrfs_send_to_file($$$;$$)
     $target_filename .= '.' . $compression{$compress->{key}}->{format};
     push @cmd_pipe, { compress => $compress }; # does nothing if already compressed by rsh_compress_out
   }
+  if($encrypt) {
+    $target_filename .= ($encrypt->{type} eq "gpg") ? '.gpg' : '.encrypted';
+  }
+
+  # NOTE: $ret_vol_received must always be set when function returns!
+  my $vol_received = vinfo_child($target, $target_filename);
+  $$ret_vol_received = $vol_received if(ref $ret_vol_received);
+
   if($encrypt) {
     $raw_info{encrypt} = $encrypt->{type};
 
@@ -1393,7 +1406,6 @@ sub btrfs_send_to_file($$$;$$)
       #   generation faster; however sometimes write operations are not
       #   desired. This option can be used to achieve that with the cost
       #   of slower random generation.
-      $target_filename .= '.gpg';
       my @gpg_options = ( '--batch', '--no-tty', '--no-random-seed-file', '--trust-model', 'always' );
       push @gpg_options, ( '--compress-algo', 'none' ) if($compress);  # NOTE: if --compress-algo is not set, gpg might still compress according to OpenPGP standard.
       push(@gpg_options, ( '--no-default-keyring', '--keyring', $encrypt->{keyring} )) if($encrypt->{keyring});
@@ -1404,6 +1416,35 @@ sub btrfs_send_to_file($$$;$$)
         compressed_ok => ($compress ? 1 : 0),
       };
     }
+    elsif($encrypt->{type} eq "openssl_enc") {
+      # encrypt using "openssl enc"
+      $raw_info{cipher} = $encrypt->{ciphername};
+
+      # NOTE: iv is always generated locally!
+      my $iv_size = $encrypt->{iv_size};
+      my $iv;
+      if($iv_size) {
+        INFO "Generating iv for openssl encryption (cipher=$encrypt->{ciphername})";
+        $iv = system_urandom($iv_size, 'hex');
+        unless($iv) {
+          ERROR "Failed generate IV for openssl_enc: $source->{PRINT}";
+          return undef;
+        }
+        $raw_info{iv} = $iv;
+      }
+
+      my @openssl_options = (
+        '-' . $encrypt->{ciphername},
+        '-K $(cat ' . $encrypt->{keyfile} . ')',
+       );
+      push @openssl_options, ('-iv', $iv) if($iv);
+
+      push @cmd_pipe, {
+        cmd => [ 'openssl', 'enc', '-e', @openssl_options ],
+        name => 'openssl_enc',
+        compressed_ok => ($compress ? 1 : 0),
+      };
+    }
     else {
       die "Usupported encryption type (raw_target_encrypt)";
     }
@@ -1442,9 +1483,6 @@ sub btrfs_send_to_file($$$;$$)
     };
   }
 
-  my $vol_received = vinfo_child($target, $target_filename);
-  $$ret_vol_received = $vol_received if(ref $ret_vol_received);
-
   $raw_info{FILE} = $target_filename;
   $raw_info{RECEIVED_PARENT_UUID} = $parent_uuid if($parent_uuid);
   # disabled for now, as its not very useful and might leak information:
@@ -1786,6 +1824,36 @@ sub system_write_raw_info($$)
 }
 
 
+sub system_urandom($;$) {
+  my $size = shift;
+  my $format = shift || 'hex';
+  die unless(($size > 0) && ($size <= 256)); # sanity check
+
+  unless(open(URANDOM, '<', '/dev/urandom')) {
+    ERROR "Failed to open /dev/urandom: $!";
+    return undef;
+  }
+  binmode URANDOM;
+  my $rand;
+  my $rlen = read(URANDOM, $rand, $size);
+  close(FILE);
+  unless(defined($rand) && ($rlen == $size)) {
+    ERROR "Failed to read from /dev/urandom: $!";
+    return undef;
+  }
+
+  if($format eq 'hex') {
+    my $hex = unpack('H*', $rand);
+    die unless(length($hex) == ($size * 2)); # paranoia check
+    return $hex;
+  }
+  elsif($format eq 'bin') {
+    return $rand;
+  }
+  die "unsupported format";
+}
+
+
 sub btr_tree($$)
 {
   my $vol = shift;
@@ -2781,6 +2849,9 @@ sub config_encrypt_hash($$)
     type => $encrypt_type,
     keyring => config_key($config, "gpg_keyring"),
     recipient => config_key($config, "gpg_recipient"),
+    iv_size => config_key($config, "openssl_iv_size"),
+    ciphername => config_key($config, "openssl_ciphername"),
+    keyfile => config_key($config, "openssl_keyfile"),
   };
 }
 

doc/btrbk.conf.5

@@ -428,18 +428,37 @@ raw_target_compress_level  default|<number>
 .PP
 raw_target_compress_threads  default|<number>
 .PP
-raw_target_encrypt  gpg|no
-.PP
 raw_target_split  <size>|no
 .PP
 raw_target_block_size  <number>  (defaults to 128K)
 .PP
+raw_target_encrypt  gpg|openssl_enc|no
+.RE
+.PD
+.PP
+Additional options for "raw_target_encrypt gpg":
+.PP
+.RS 4
 gpg_keyring  <file>
+.PD 0
 .PP
 gpg_recipient  <name>
 .RE
 .PD
 .PP
+Additional options for "raw_target_encrypt openssl_enc" (\fIvery
+experimental\fR):
+.PP
+.RS 4
+openssl_ciphername  <name>  (defaults to "aes-256-cbc")
+.PD 0
+.PP
+openssl_iv_size  <size-in-bytes>|no  (depends on selected cipher)
+.PP
+openssl_keyfile  <file>|no
+.RE
+.PD
+.PP
 Raw backups consist of two files: the main data file containing the
 btrfs send stream, and a sidecar file ".info" containing metadata:
 .RS 4