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Merge pull request #4597 from ehmry/cjdns

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Cjdns
This commit is contained in:
Aristid Breitkreuz 2014-10-22 20:49:20 +02:00
parent 69989eea1b a3338abcfe
commit 608aeede89
5 changed files with 426 additions and 156 deletions
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11
nixos/modules/services/networking/cjdns-hosts.sh Normal file
View file

@ -0,0 +1,11 @@
pubs=($pubs)
hosts=($hosts)
lines="''\n"
for ((i = 0; i < ${#pubs[*]}; i++)); do
addr=$($cjdns/bin/publictoip6 ${pubs[i]})
lines="${lines}$addr ${hosts[i]}\n"
done
lines="${lines}''"
echo -ne $lines > $out

194
nixos/modules/services/networking/cjdns.nix
View file

@ -4,8 +4,46 @@ with lib;
let
pkg = pkgs.cjdns;
cfg = config.services.cjdns;
connectToSubmodule =
{ options, ... }:
{ options =
{ password = mkOption {
type = types.str;
description = "Authorized password to the opposite end of the tunnel.";
};
publicKey = mkOption {
type = types.str;
description = "Public key at the opposite end of the tunnel.";
};
hostname = mkOption {
default = "";
example = "foobar.hype";
type = types.str;
description = "Optional hostname to add to /etc/hosts; prevents reverse lookup failures.";
};
};
};
peers = mapAttrsToList (n: v: v) (cfg.ETHInterface.connectTo // cfg.UDPInterface.connectTo);
pubs = toString (map (p: if p.hostname == "" then "" else p.publicKey) peers);
hosts = toString (map (p: if p.hostname == "" then "" else p.hostname) peers);
cjdnsHosts =
if hosts != "" then
import (pkgs.stdenv.mkDerivation {
name = "cjdns-hosts";
builder = ./cjdns-hosts.sh;
inherit (pkgs) cjdns;
inherit pubs hosts;
})
else "";
# would be nice to merge 'cfg' with a //,
# but the json nesting is wacky.
cjdrouteConf = builtins.toJSON ( {
@ -44,7 +82,7 @@ in
enable = mkOption {
type = types.bool;
default = false;
default = false;
description = ''
Whether to enable the cjdns network encryption
and routing engine. A file at /etc/cjdns.keys will
@ -53,84 +91,80 @@ in
'';
};
confFile = mkOption {
type = types.str;
default = "";
example = "/etc/cjdroute.conf";
description = ''
Ignore all other cjdns options and load configuration from this file.
'';
};
authorizedPasswords = mkOption {
type = types.listOf types.str;
default = [ ];
example = [
default = [ ];
example = [
"snyrfgkqsc98qh1y4s5hbu0j57xw5s0"
"z9md3t4p45mfrjzdjurxn4wuj0d8swv"
"49275fut6tmzu354pq70sr5b95qq0vj"
"z9md3t4p45mfrjzdjurxn4wuj0d8swv"
"49275fut6tmzu354pq70sr5b95qq0vj"
];
description = ''
Any remote cjdns nodes that offer these passwords on
connection will be allowed to route through this node.
description = ''
Any remote cjdns nodes that offer these passwords on
connection will be allowed to route through this node.
'';
};
admin = {
bind = mkOption {
type = types.string;
default = "127.0.0.1:11234";
description = ''
default = "127.0.0.1:11234";
description = ''
Bind the administration port to this address and port.
'';
'';
};
};
UDPInterface = {
bind = mkOption {
type = types.string;
default = "";
default = "";
example = "192.168.1.32:43211";
description = ''
Address and port to bind UDP tunnels to.
'';
};
Address and port to bind UDP tunnels to.
'';
};
connectTo = mkOption {
type = types.attrsOf ( types.submodule (
{ options, ... }:
{ options = {
# TODO make host an option, and add it to networking.extraHosts
password = mkOption {
type = types.str;
description = "Authorized password to the opposite end of the tunnel.";
};
publicKey = mkOption {
type = types.str;
description = "Public key at the opposite end of the tunnel.";
};
};
}
));
default = { };
type = types.attrsOf ( types.submodule ( connectToSubmodule ) );
default = { };
example = {
"192.168.1.1:27313" = {
password = "5kG15EfpdcKNX3f2GSQ0H1HC7yIfxoCoImnO5FHM";
hostname = "homer.hype";
password = "5kG15EfpdcKNX3f2GSQ0H1HC7yIfxoCoImnO5FHM";
publicKey = "371zpkgs8ss387tmr81q04mp0hg1skb51hw34vk1cq644mjqhup0.k";
};
};
description = ''
Credentials for making UDP tunnels.
'';
};
Credentials for making UDP tunnels.
'';
};
};
ETHInterface = {
bind = mkOption {
default = "";
example = "eth0";
description = ''
Bind to this device for native ethernet operation.
'';
};
default = "";
example = "eth0";
description = ''
Bind to this device for native ethernet operation.
'';
};
beacon = mkOption {
type = types.int;
type = types.int;
default = 2;
description = ''
Auto-connect to other cjdns nodes on the same network.
Options:
0: Disabled.
0: Disabled.
1: Accept beacons, this will cause cjdns to accept incoming
beacon messages and try connecting to the sender.
2: Accept and send beacons, this will cause cjdns to broadcast
@ -142,32 +176,20 @@ in
};
connectTo = mkOption {
type = types.attrsOf ( types.submodule (
{ options, ... }:
{ options = {
password = mkOption {
type = types.str;
description = "Authorized password to the opposite end of the tunnel.";
};
publicKey = mkOption {
type = types.str;
description = "Public key at the opposite end of the tunnel.";
};
};
}
));
default = { };
type = types.attrsOf ( types.submodule ( connectToSubmodule ) );
default = { };
example = {
"01:02:03:04:05:06" = {
password = "5kG15EfpdcKNX3f2GSQ0H1HC7yIfxoCoImnO5FHM";
hostname = "homer.hype";
password = "5kG15EfpdcKNX3f2GSQ0H1HC7yIfxoCoImnO5FHM";
publicKey = "371zpkgs8ss387tmr81q04mp0hg1skb51hw34vk1cq644mjqhup0.k";
};
};
description = ''
Credentials for connecting look similar to UDP credientials
description = ''
Credentials for connecting look similar to UDP credientials
except they begin with the mac address.
'';
};
'';
};
};
};
@ -185,34 +207,48 @@ in
wantedBy = [ "multi-user.target" ];
after = [ "network-interfaces.target" ];
script = ''
source /etc/cjdns.keys
echo '${cjdrouteConf}' | sed \
-e "s/@CJDNS_ADMIN_PASSWORD@/$CJDNS_ADMIN_PASSWORD/g" \
-e "s/@CJDNS_PRIVATE_KEY@/$CJDNS_PRIVATE_KEY/g" \
| ${pkgs.cjdns}/bin/cjdroute
'';
script = (
if cfg.confFile != "" then "${pkg}/bin/cjdroute < ${cfg.confFile}" else
''
source /etc/cjdns.keys
echo '${cjdrouteConf}' | sed \
-e "s/@CJDNS_ADMIN_PASSWORD@/$CJDNS_ADMIN_PASSWORD/g" \
-e "s/@CJDNS_PRIVATE_KEY@/$CJDNS_PRIVATE_KEY/g" \
| ${pkg}/bin/cjdroute
''
);
serviceConfig = {
Type = "forking";
Restart = "on-failure";
Restart = "on-failure";
};
};
system.activationScripts.cjdns = ''
system.activationScripts.cjdns = if (cfg.confFile == "") then "" else ''
cjdnsWriteKeys() {
private=$1
ipv6=$2
public=$3
echo "CJDNS_PRIVATE_KEY=$1" >> /etc/cjdns.keys
echo -e "CJDNS_IPV6=$2\nCJDNS_PUBLIC_KEY=$3" > /etc/cjdns.public
chmod 600 /etc/cjdns.keys
chmod 444 /etc/cjdns.public
}
grep -q "CJDNS_PRIVATE_KEY=" /etc/cjdns.keys || \
echo "CJDNS_PRIVATE_KEY=$(${pkgs.cjdns}/bin/makekey)" \
>> /etc/cjdns.keys
cjdnsWriteKeys $(${pkg}/bin/makekeys)
grep -q "CJDNS_ADMIN_PASSWORD=" /etc/cjdns.keys || \
echo "CJDNS_ADMIN_PASSWORD=$(${pkgs.coreutils}/bin/head -c 96 /dev/urandom | ${pkgs.coreutils}/bin/tr -dc A-Za-z0-9)" \
>> /etc/cjdns.keys
chmod 600 /etc/cjdns.keys
echo "CJDNS_ADMIN_PASSWORD=$(${pkgs.coreutils}/bin/head -c 96 /dev/urandom | ${pkgs.coreutils}/bin/tr -dc A-Za-z0-9)" \
>> /etc/cjdns.keys
'';
networking.extraHosts = "${cjdnsHosts}";
assertions = [
{ assertion = ( cfg.ETHInterface.bind != "" || cfg.UDPInterface.bind != "" );
{ assertion = ( cfg.ETHInterface.bind != "" || cfg.UDPInterface.bind != "" || cfg.confFile == "" );
message = "Neither cjdns.ETHInterface.bind nor cjdns.UDPInterface.bind defined.";
}
{ assertion = config.networking.enableIPv6;

27
pkgs/tools/networking/cjdns/default.nix
View file

@ -1,30 +1,31 @@
{ stdenv, fetchgit, nodejs, which, python27 }:
{ stdenv, fetchFromGitHub, nodejs, which, python27 }:
let
date = "20140922";
rev = "5ebca772b0582173127e8c1e61ee235c5ab3fb50";
date = "20140928";
rev = "e2b673698e471dbc82b4e9dbc04cb9e16f1f06a6";
in
stdenv.mkDerivation {
name = "cjdns-${date}-${stdenv.lib.strings.substring 0 7 rev}";
src = fetchgit {
url = "https://github.com/cjdelisle/cjdns.git";
src = fetchFromGitHub {
owner = "cjdelisle";
repo = "cjdns";
inherit rev;
sha256 = "04abf73f4aede12c35b70ae09a367b3d6352a63f818185f788ed13356d06197a";
sha256 = "0ql51845rni6678dda03zr18ary7xlqcs3khva9x80x815h1sy8v";
};
patches = [ ./rfc5952.patch ];
buildInputs = [ which python27 nodejs];
patches = [ ./makekey.patch ];
buildPhase = "bash do";
installPhase = "installBin cjdroute makekey";
installPhase = "installBin cjdroute makekeys privatetopublic publictoip6";
meta = {
meta = with stdenv.lib; {
homepage = https://github.com/cjdelisle/cjdns;
description = "Encrypted networking for regular people";
license = stdenv.lib.licenses.gpl3;
maintainers = with stdenv.lib.maintainers; [ viric emery ];
platforms = stdenv.lib.platforms.linux;
license = licenses.gpl3;
maintainers = with maintainers; [ viric emery ];
platforms = platforms.unix;
};
}

64
pkgs/tools/networking/cjdns/makekey.patch
View file

@ -1,64 +0,0 @@
diff --git a/contrib/c/makekey.c b/contrib/c/makekey.c
new file mode 100644
index 0000000..c7184e5
--- /dev/null
+++ b/contrib/c/makekey.c
@@ -0,0 +1,46 @@
+/* vim: set expandtab ts=4 sw=4: */
+/*
+ * You may redistribute this program and/or modify it under the terms of
+ * the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "crypto/random/Random.h"
+#include "memory/MallocAllocator.h"
+#include "crypto/AddressCalc.h"
+#include "util/AddrTools.h"
+#include "util/Hex.h"
+
+#include "crypto_scalarmult_curve25519.h"
+
+#include <stdio.h>
+
+int main(int argc, char** argv)
+{
+ struct Allocator* alloc = MallocAllocator_new(1<<22);
+ struct Random* rand = Random_new(alloc, NULL, NULL);
+
+ uint8_t privateKey[32];
+ uint8_t publicKey[32];
+ uint8_t ip[16];
+ uint8_t hexPrivateKey[65];
+
+ for (;;) {
+ Random_bytes(rand, privateKey, 32);
+ crypto_scalarmult_curve25519_base(publicKey, privateKey);
+ if (AddressCalc_addressForPublicKey(ip, publicKey)) {
+ Hex_encode(hexPrivateKey, 65, privateKey, 32);
+ printf(hexPrivateKey);
+ return 0;
+ }
+ }
+ return 0;
+}
+
diff --git a/node_build/make.js b/node_build/make.js
index 5e51645..11465e3 100644
--- a/node_build/make.js
+++ b/node_build/make.js
@@ -339,6 +339,7 @@ Builder.configure({
builder.buildExecutable('contrib/c/privatetopublic.c');
builder.buildExecutable('contrib/c/sybilsim.c');
builder.buildExecutable('contrib/c/makekeys.c');
+ builder.buildExecutable('contrib/c/makekey.c');
builder.buildExecutable('crypto/random/randombytes.c');

286
pkgs/tools/networking/cjdns/rfc5952.patch Normal file
View file

@ -0,0 +1,286 @@
diff --git a/admin/angel/cjdroute2.c b/admin/angel/cjdroute2.c
index dfce6c6..77954a7 100644
--- a/admin/angel/cjdroute2.c
+++ b/admin/angel/cjdroute2.c
@@ -80,7 +80,7 @@ static int genAddress(uint8_t addressOut[40],
if (AddressCalc_addressForPublicKey(address.ip6.bytes, address.key)) {
Hex_encode(privateKeyHexOut, 65, privateKey, 32);
Base32_encode(publicKeyBase32Out, 53, address.key, 32);
- Address_printIp(addressOut, &address);
+ Address_printShortIp(addressOut, &address);
return 0;
}
}
diff --git a/contrib/c/makekeys.c b/contrib/c/makekeys.c
index 3727fff..29582f1 100644
--- a/contrib/c/makekeys.c
+++ b/contrib/c/makekeys.c
@@ -41,7 +41,7 @@ int main(int argc, char** argv)
if (AddressCalc_addressForPublicKey(ip, publicKey)) {
Hex_encode(hexPrivateKey, 65, privateKey, 32);
Base32_encode(publicKeyBase32, 53, publicKey, 32);
- AddrTools_printIp(printedIp, ip);
+ AddrTools_printShortIp(printedIp, ip);
printf("%s %s %s.k\n", hexPrivateKey, printedIp, publicKeyBase32);
}
}
diff --git a/contrib/c/privatetopublic.c b/contrib/c/privatetopublic.c
index 7f5f967..dc98f1c 100644
--- a/contrib/c/privatetopublic.c
+++ b/contrib/c/privatetopublic.c
@@ -73,7 +73,7 @@ int main(int argc, char** argv)
AddressCalc_addressForPublicKey(address.ip6.bytes, address.key);
if (address.ip6.bytes[0] == 0xFC) {
Base32_encode(publicKeyBase32Out, 53, address.key, 32);
- Address_printIp(addressOut, &address);
+ Address_printShortIp(addressOut, &address);
printf( "Input privkey: %s\n"
"Matching pubkey: %s.k\n"
"Resulting address: %s\n"
diff --git a/contrib/c/publictoip6.c b/contrib/c/publictoip6.c
index fc92f7e..99afc4c 100644
--- a/contrib/c/publictoip6.c
+++ b/contrib/c/publictoip6.c
@@ -48,7 +48,7 @@ int main(int argc, char** argv)
}
uint8_t output[40] = {0};
- AddrTools_printIp(output, ip6Bytes);
+ AddrTools_printShortIp(output, ip6Bytes);
printf("%s\n", output);
return 0;
}
diff --git a/dht/Address.c b/dht/Address.c
index e4c2dba..ba77cad 100644
--- a/dht/Address.c
+++ b/dht/Address.c
@@ -102,6 +102,12 @@ void Address_printIp(uint8_t output[40], struct Address* addr)
AddrTools_printIp(output, addr->ip6.bytes);
}
+void Address_printShortIp(uint8_t output[40], struct Address* addr)
+{
+ Address_getPrefix(addr);
+ AddrTools_printShortIp(output, addr->ip6.bytes);
+}
+
void Address_print(uint8_t output[60], struct Address* addr)
{
Address_printIp(output, addr);
diff --git a/dht/Address.h b/dht/Address.h
index 43c6f05..f200b40 100644
--- a/dht/Address.h
+++ b/dht/Address.h
@@ -94,6 +94,8 @@ void Address_forKey(struct Address* out, const uint8_t key[Address_KEY_SIZE]);
void Address_printIp(uint8_t output[40], struct Address* addr);
+void Address_printShortIp(uint8_t output[40], struct Address* addr);
+
void Address_print(uint8_t output[60], struct Address* addr);
String* Address_toString(struct Address* addr, struct Allocator* alloc);
diff --git a/net/Ducttape.c b/net/Ducttape.c
index 84597d0..1813f3f 100644
--- a/net/Ducttape.c
+++ b/net/Ducttape.c
@@ -227,7 +227,7 @@ static inline bool isRouterTraffic(struct Message* message, struct Headers_IP6He
#define debugHandles(logger, session, message, ...) \
do { \
uint8_t ip[40]; \
- AddrTools_printIp(ip, session->ip6); \
+ AddrTools_printIp(ip, session->ip6); \
Log_debug(logger, "ver[%u] send[%d] recv[%u] ip[%s] " message, \
session->version, \
Endian_hostToBigEndian32(session->sendHandle_be), \
@@ -271,10 +271,10 @@ static inline uint8_t incomingForMe(struct Message* message,
if (Bits_memcmp(addr.ip6.bytes, dtHeader->ip6Header->sourceAddr, 16)) {
#ifdef Log_DEBUG
uint8_t keyAddr[40];
- Address_printIp(keyAddr, &addr);
+ Address_printShortIp(keyAddr, &addr);
Bits_memcpyConst(addr.ip6.bytes, dtHeader->ip6Header->sourceAddr, 16);
uint8_t srcAddr[40];
- Address_printIp(srcAddr, &addr);
+ Address_printShortIp(srcAddr, &addr);
Log_debug(context->logger,
"DROP packet because source address is not same as key.\n"
" %s source addr\n"
@@ -292,7 +292,7 @@ static inline uint8_t incomingForMe(struct Message* message,
if (Checksum_udpIp6(dtHeader->ip6Header->sourceAddr, (uint8_t*)uh, message->length)) {
#ifdef Log_DEBUG
uint8_t keyAddr[40];
- Address_printIp(keyAddr, &addr);
+ Address_printShortIp(keyAddr, &addr);
Log_debug(context->logger,
"DROP Router packet with incorrect checksum, from [%s]", keyAddr);
#endif
@@ -708,7 +708,7 @@ static inline int core(struct Message* message,
struct Address destination;
Bits_memcpyConst(destination.ip6.bytes, ip6Header->destinationAddr, 16);
uint8_t ipAddr[40];
- Address_printIp(ipAddr, &destination);
+ Address_printShortIp(ipAddr, &destination);
Log_debug(context->logger, "Forwarding data to %s via %s\n", ipAddr, nhAddr);
#endif */
} else {
@@ -723,7 +723,7 @@ static inline int core(struct Message* message,
struct Address destination;
Bits_memcpyConst(destination.ip6.bytes, ip6Header->destinationAddr, 16);
uint8_t ipAddr[40];
- Address_printIp(ipAddr, &destination);
+ Address_printShortIp(ipAddr, &destination);
Log_info(context->logger, "DROP message because this node is the closest known "
"node to the destination %s.", ipAddr);
#endif
diff --git a/test/printIp_test.c b/test/printIp_test.c
new file mode 100644
index 0000000..75d7427
--- /dev/null
+++ b/test/printIp_test.c
@@ -0,0 +1,54 @@
+/* vim: set expandtab ts=4 sw=4: */
+/*
+ * You may redistribute this program and/or modify it under the terms of
+ * the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "crypto/random/Random.h"
+#include "memory/MallocAllocator.h"
+#include "util/AddrTools.h"
+#include "util/Assert.h"
+
+#include <stdio.h>
+
+int main()
+{
+ struct Allocator* alloc = MallocAllocator_new(1<<22);
+ struct Random* rand = Random_new(alloc, NULL, NULL);
+
+ uint8_t ip[16];
+ uint8_t printedIp[40];
+ uint8_t printedShortIp[40];
+ uint8_t ipFromFull[16];
+ uint8_t ipFromShort[16];
+
+ for (int i = 0; i < 1024; ++i) {
+ Random_bytes(rand, ip, 16);
+
+ for (int j = 0; j < 16; j++) {
+ // make the random result have lots of zeros since that's what we're looking for.
+ ip[j] = (ip[j] % 2) ? 0 : ip[j];
+ }
+
+ AddrTools_printIp(printedIp, ip);
+ AddrTools_printShortIp(printedShortIp, ip);
+ //printf("%s\n%s\n\n", printedIp, printedShortIp);
+
+ AddrTools_parseIp(ipFromFull, printedIp);
+ AddrTools_parseIp(ipFromShort, printedShortIp);
+
+ Assert_true(0 == Bits_memcmp(ip, ipFromFull, 16));
+ Assert_true(0 == Bits_memcmp(ipFromFull, ipFromShort, 16));
+ }
+
+ return 0;
+}
diff --git a/util/AddrTools.h b/util/AddrTools.h
index 858ced4..d59544d 100644
--- a/util/AddrTools.h
+++ b/util/AddrTools.h
@@ -143,6 +143,44 @@ static inline void AddrTools_printIp(uint8_t output[40], const uint8_t binIp[16]
output[39] = '\0';
}
+static inline void AddrTools_printShortIp(uint8_t output[40], const uint8_t binIp[16])
+{
+ /* The chances of hitting :0:0: and breaking
+ * RFC5952 are 1 in (1 / (2^16))^2 * 6.
+ * E. Siler
+ */
+
+ char *p = output;
+ int i = 0;
+ for (; i < 16;) {
+ if ((size_t)p != (size_t)output) {
+ *p++= ':';
+ }
+
+ if (binIp[i] > 0x0F) {
+ Hex_encode(p, 2, &binIp[i++], 1);
+ p += 2;
+ } else if (binIp[i] > 0x00) {
+ *p++ = Hex_encodeLowNibble(binIp[i++]);
+ } else {
+ ++i;
+ if (binIp[i] > 0x0F) {
+ Hex_encode(p, 2, &binIp[i++], 1);
+ p += 2;
+ } else {
+ *p++ = Hex_encodeLowNibble(binIp[i++]);
+ }
+ continue;
+ }
+ Hex_encode(p, 2, &binIp[i++], 1);
+ p += 2;
+ }
+ *p = '\0';
+
+ Assert_true((size_t)p <= ((size_t)output + 40));
+ Assert_true(i <= 16);
+}
+
/**
* Parse out an address.
*
diff --git a/util/Hex.c b/util/Hex.c
index e3e3c4d..b9bce57 100644
--- a/util/Hex.c
+++ b/util/Hex.c
@@ -29,6 +29,8 @@ static const uint8_t numForAscii[] =
99,99,99,99,99,99,99,99,99,99,99,99,99,99,99,99,
};
+static const char* hexEntities = "0123456789abcdef";
+
int Hex_encode(uint8_t* output,
const uint32_t outputLength,
const uint8_t* in,
@@ -40,8 +42,6 @@ int Hex_encode(uint8_t* output,
output[inputLength * 2] = '\0';
}
- static const char* hexEntities = "0123456789abcdef";
-
for (uint32_t i = 0; i < inputLength; i++) {
output[i * 2] = hexEntities[in[i] >> 4];
output[i * 2 + 1] = hexEntities[in[i] & 15];
@@ -88,3 +88,8 @@ int Hex_decode(uint8_t* output,
return length / 2;
}
+
+uint8_t Hex_encodeLowNibble(const uint8_t nibble)
+{
+ return hexEntities[nibble & 15];
+}
diff --git a/util/Hex.h b/util/Hex.h
index 4570c3e..a12e402 100644
--- a/util/Hex.h
+++ b/util/Hex.h
@@ -41,4 +41,6 @@ bool Hex_isHexEntity(const uint8_t character);
int Hex_decodeByte(const uint8_t highNibble, const uint8_t lowNibble);
+uint8_t Hex_encodeLowNibble(const uint8_t nibble);
+
#endif