From 8dfa072733feab737cabf69f000c70657719826a Mon Sep 17 00:00:00 2001 From: Guus Sliepen Date: Sun, 3 Jul 2011 13:17:28 +0200 Subject: [PATCH] Support ECDH key exchange. REQ_KEY requests have an extra field indicating key exchange version. If it is present and > 0, the sender supports ECDH. If the receiver also does, then it will generate a new keypair and sends the public key in a ANS_KEY request with "ECDH:" prefixed. The ans_key_h() function will compute the shared secret, which, at the moment,is used as is to set the cipher and HMAC keys. However, this must be changed to use a proper KDF. In the future, the ECDH key exchange must also be signed. --- src/node.h | 6 ++- src/openssl/ecdh.h | 1 + src/protocol_key.c | 129 ++++++++++++++++++++++++++++++++++++++++----- 3 files changed, 122 insertions(+), 14 deletions(-) diff --git a/src/node.h b/src/node.h index 2f08186..05d751c 100644 --- a/src/node.h +++ b/src/node.h @@ -25,6 +25,7 @@ #include "cipher.h" #include "connection.h" #include "digest.h" +#include "ecdh.h" #include "subnet.h" typedef struct node_status_t { @@ -34,7 +35,8 @@ typedef struct node_status_t { unsigned int visited:1; /* 1 if this node has been visited by one of the graph algorithms */ unsigned int reachable:1; /* 1 if this node is reachable in the graph */ unsigned int indirect:1; /* 1 if this node is not directly reachable by us */ - unsigned int unused:26; + unsigned int ecdh:1; /* 1 if this node supports ECDH key exchange */ + unsigned int unused:25; } node_status_t; typedef struct node_t { @@ -47,6 +49,8 @@ typedef struct node_t { node_status_t status; time_t last_req_key; + ecdh_t ecdh; /* State for ECDH key exchange */ + cipher_t incipher; /* Cipher for UDP packets */ digest_t indigest; /* Digest for UDP packets */ diff --git a/src/openssl/ecdh.h b/src/openssl/ecdh.h index c5b43d8..bf32266 100644 --- a/src/openssl/ecdh.h +++ b/src/openssl/ecdh.h @@ -23,6 +23,7 @@ #include #define ECDH_SIZE 67 +#define ECDH_SHARED_SIZE 66 typedef EC_KEY *ecdh_t; diff --git a/src/protocol_key.c b/src/protocol_key.c index 1e7aa03..f52e896 100644 --- a/src/protocol_key.c +++ b/src/protocol_key.c @@ -24,6 +24,7 @@ #include "cipher.h" #include "connection.h" #include "crypto.h" +#include "ecdh.h" #include "logger.h" #include "net.h" #include "netutl.h" @@ -82,15 +83,16 @@ bool key_changed_h(connection_t *c, char *request) { } bool send_req_key(node_t *to) { - return send_request(to->nexthop->connection, "%d %s %s", REQ_KEY, myself->name, to->name); + return send_request(to->nexthop->connection, "%d %s %s 1", REQ_KEY, myself->name, to->name); } bool req_key_h(connection_t *c, char *request) { char from_name[MAX_STRING_SIZE]; char to_name[MAX_STRING_SIZE]; node_t *from, *to; + int kx_version = 0; - if(sscanf(request, "%*d " MAX_STRING " " MAX_STRING, from_name, to_name) != 2) { + if(sscanf(request, "%*d " MAX_STRING " " MAX_STRING " %d", from_name, to_name, &kx_version) < 2) { logger(LOG_ERR, "Got bad %s from %s (%s)", "REQ_KEY", c->name, c->hostname); return false; @@ -120,7 +122,10 @@ bool req_key_h(connection_t *c, char *request) { /* Check if this key request is for us */ if(to == myself) { /* Yes, send our own key back */ - + if(kx_version > 0) { + logger(LOG_DEBUG, "Got ECDH key request from %s", from->name); + from->status.ecdh = true; + } send_ans_key(from); } else { if(tunnelserver) @@ -138,7 +143,26 @@ bool req_key_h(connection_t *c, char *request) { return true; } +bool send_ans_key_ecdh(node_t *to) { + char key[ECDH_SIZE * 2 + 1]; + + ecdh_generate_public(&to->ecdh, key); + + bin2hex(key, key, ECDH_SIZE); + key[ECDH_SIZE * 2] = '\0'; + + return send_request(to->nexthop->connection, "%d %s %s ECDH:%s %d %d %zu %d", ANS_KEY, + myself->name, to->name, key, + cipher_get_nid(&myself->incipher), + digest_get_nid(&myself->indigest), + digest_length(&myself->indigest), + myself->incompression); +} + bool send_ans_key(node_t *to) { + if(to->status.ecdh) + return send_ans_key_ecdh(to); + size_t keylen = cipher_keylength(&myself->incipher); char key[keylen * 2 + 1]; @@ -175,7 +199,7 @@ bool ans_key_h(connection_t *c, char *request) { int cipher, digest, maclength, compression, keylen; node_t *from, *to; - if(sscanf(request, "%*d "MAX_STRING" "MAX_STRING" "MAX_STRING" %d %d %d %d "MAX_STRING" "MAX_STRING, + if(sscanf(request, "%*d "MAX_STRING" "MAX_STRING" "MAX_STRING" %d %d %d %d "MAX_STRING" "MAX_STRING" %d", from_name, to_name, key, &cipher, &digest, &maclength, &compression, address, port) < 7) { logger(LOG_ERR, "Got bad %s from %s (%s)", "ANS_KEY", c->name, @@ -236,13 +260,6 @@ bool ans_key_h(connection_t *c, char *request) { return false; } - keylen = strlen(key) / 2; - - if(keylen != cipher_keylength(&from->outcipher)) { - logger(LOG_ERR, "Node %s (%s) uses wrong keylength!", from->name, from->hostname); - return false; - } - if(!digest_open_by_nid(&from->outdigest, digest, maclength)) { logger(LOG_ERR, "Node %s (%s) uses unknown digest!", from->name, from->hostname); return false; @@ -257,12 +274,98 @@ bool ans_key_h(connection_t *c, char *request) { logger(LOG_ERR, "Node %s (%s) uses bogus compression level!", from->name, from->hostname); return true; } - + from->outcompression = compression; + /* ECDH or old-style key exchange? */ + /* TODO: look at SSH and TLS to see how they derive cipher and HMAC keys from shared secret properly */ + + if(!strncmp(key, "ECDH:", 5)) { + logger(LOG_DEBUG, "Got ECDH key from %s", from->name); + + keylen = (strlen(key) - 5) / 2; + + if(keylen != ECDH_SIZE) { + logger(LOG_ERR, "Node %s (%s) uses wrong keylength!", from->name, from->hostname); + return false; + } + + if(ECDH_SHARED_SIZE < cipher_keylength(&from->outcipher)) { + logger(LOG_ERR, "ECDH key too short for cipher of %s!", from->name); + return false; + } + + if(!from->ecdh) { + logger(LOG_DEBUG, "Woops, we didn't generate our public key yet"); + from->status.ecdh = true; + if(!send_ans_key(from)) + return false; + } + + char shared[ECDH_SHARED_SIZE * 2 + 1]; + char hex[ECDH_SHARED_SIZE * 2 + 1]; + hex2bin(key + 5, key + 5, keylen); + + if(!ecdh_compute_shared(&from->ecdh, key + 5, shared)) + return false; + + /* Update our crypto end */ + + char *mykey; + size_t mykeylen = cipher_keylength(&myself->incipher); + keylen = cipher_keylength(&from->outcipher); + + if(ECDH_SHARED_SIZE < mykeylen) { + logger(LOG_ERR, "ECDH key too short for cipher of MYSELF!"); + return false; + } + + if(strcmp(myself->name, from->name) < 0) { + logger(LOG_DEBUG, "Using left half of shared secret"); + mykey = shared; + memcpy(key, shared + ECDH_SHARED_SIZE - keylen, keylen); + } else { + logger(LOG_DEBUG, "Using right half of shared secret"); + mykey = shared + ECDH_SHARED_SIZE - mykeylen; + memcpy(key, shared, keylen); + } + + cipher_open_by_nid(&from->incipher, cipher_get_nid(&myself->incipher)); + digest_open_by_nid(&from->indigest, digest_get_nid(&myself->indigest), digest_length(&myself->indigest)); + from->incompression = myself->incompression; + + cipher_set_key(&from->incipher, mykey, true); + digest_set_key(&from->indigest, mykey, mykeylen); + + // Reset sequence number and late packet window + mykeyused = true; + from->received_seqno = 0; + if(replaywin) + memset(from->late, 0, replaywin); + + bin2hex(shared, hex, ECDH_SHARED_SIZE); + hex[ECDH_SHARED_SIZE * 2] = 0; + logger(LOG_DEBUG, "Shared secret was %s", hex); + + bin2hex(mykey, hex, mykeylen); + hex[mykeylen * 2] = 0; + logger(LOG_DEBUG, "My part is: %s (%d)", hex, mykeylen); + + bin2hex(key, hex, keylen); + hex[keylen * 2] = 0; + logger(LOG_DEBUG, "His part is: %s (%d)", hex, keylen); + } else { + keylen = strlen(key) / 2; + hex2bin(key, key, keylen); + } + /* Update our copy of the origin's packet key */ - hex2bin(key, key, keylen); + if(keylen != cipher_keylength(&from->outcipher)) { + logger(LOG_ERR, "Node %s (%s) uses wrong keylength!", from->name, from->hostname); + return false; + } + cipher_set_key(&from->outcipher, key, false); digest_set_key(&from->outdigest, key, keylen); -- 2.25.1