2 files changed, 305 insertions, 2 deletions

diff --git a/Makefile b/Makefile
index 631717d..3864298 100644
--- a/Makefile
+++ b/Makefile
@@ -3,8 +3,8 @@ all: sender receiver
 sender: sender.c
         $(CC) -o sender sender.c -lmbedtls -lmbedcrypto
 
-receiver: receiver.c
-        $(CC) -o receiver receiver.c -lmbedtls -lmbedcrypto
+receiver: receiver.cpp
+        $(CC) -std=c++17 -o receiver receiver.cpp -lmbedtls -lmbedcrypto -lc++
 
 clean:
         rm -f sender receiver
diff --git a/receiver.cpp b/receiver.cpp
new file mode 100644
index 0000000..fdeee05
--- /dev/null
+++ b/receiver.cpp
@@ -0,0 +1,303 @@
+#include <regex.h>
+#include <string.h>
+#include <dirent.h>
+#include <err.h>
+#include <stdio.h>
+#include <inttypes.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+
+#include <mbedtls/pk.h>
+#include <mbedtls/entropy.h>
+#include "mbedtls/ctr_drbg.h"
+#include "mbedtls/gcm.h"
+
+#include <string>
+#include <map>
+#include <iostream>
+
+const unsigned short PORT = 58132;
+
+static const unsigned char privkey[] =
+"-----BEGIN RSA PRIVATE KEY-----\n"
+"MIIEpAIBAAKCAQEAwWlNmLHOOzZpdrfp+EAANwqab0FhQwCyZ/u+ySBW5XxPf6mo\n"
+"bySvtJrLdsWzdwnup/UfwZiEhJk/4wpD4Qf/2+syuJi3Rf7L+Jfh//Qf9uXAS80+\n"
+"LYad7dW0c1r5nt+F9Can5fBn7futnd8n672T+y8QpHRwX9GtaILvYQe5GQac8cfq\n"
+"2rGUd5iYj5KSdcaIZnJ4YgnjLHg2PMbtEJwqcV+2oAkcOPzTAJoNE7XjLZTwXmLl\n"
+"FgL/2cN4uJZBDnwv3RZSAhpdYF4KOJmE2GFs2jdvRUrYO7WSl8fM16vRH4vz5MNN\n"
+"caprg2MlXheVTPQa+WMdcz7dyQx8s9kRVPPUSwIDAQABAoIBAH1KD8A4flYRO2Ry\n"
+"YxgzrW/6aGxlt/HFg8ykYcS8NE5Yps8WQkwtQb0HAYKhM06LmpQm0DmC6WVUOPSE\n"
+"c9BUdEQsKiE2nJK1KcCR8w7xP7uavWTdQcgQCkJFS63mYwmt1oKAgAcOIuUhQiig\n"
+"pKWrmy7+IBPIcftAQssO9q6uaBNy+ONu6KU/FYd4UAoEt07MzuIAl5rybROOWCrA\n"
+"cjuOKK830Q2Mi2ESwwlO0+3Vyz9VhSha5wW2WwFv9zx8YQblaVXxfXC6O5XcXb0j\n"
+"O2rTpgHMmOVik3Zrg3XoRXsNZCvFQqbIevwGhRNEFQTnzakh/5g0VDa54RAK/APC\n"
+"t3ABEAECgYEA+rnqDqmXQc/xMCLOhJduxRFvZbT6EbUVJG5+l6XtATTa4LWzqx1B\n"
+"QDXS/Dixxc9FA1vSH2rAW//6wbr8KXihSeI7YxgIfWyrSIxbS3Dd1qwddvniYIpx\n"
+"ms9vYpQKAewv2p310nf7fyuURES8YikhpSuff3DhzXBEi7s3Y7gIIEsCgYEAxXrD\n"
+"6xjgLSgbbdyqxKeNk8ADMifbj8ZoiNIHkJ6sShFaTEbyHweOJ4RY7OmTBUDhgzUY\n"
+"1oynztilADFaq8KhsiMqzI3DgZ3/2OElGYReEAbXljvgudL3tmiBWc5j9S7XNLBe\n"
+"u9f3WYAYDu7/BVqmQWa/QtD9JquoZ1xgV2D6nAECgYEA29w9t9/VSJvM9xX+nNyi\n"
+"AON6GOjrRK3TPWA7WEXjH+S2bshHJi0ANAs+2Xfpw/kunnRdPLmCtuowfMO4LbGf\n"
+"VcexpgLEJyAszvBteikeDwpcyCD19wxP9J4kIYCJiggQKpfLoWUfP/P6DydrPnSt\n"
+"EUbAlaNqDpl9Mj7YonQVhCMCgYEAv0c9M5+hrDuX7d76zYaZvI4UymUO54E/yZ7e\n"
+"UvdOXGPYed+SL/oKeD5aQAeyLzl79bHdgBs3g0QW9kvXzly0cC5eC0oZH5hhs7nI\n"
+"TKII1i86bLtM3dD5vQYWnF0sNtWK/+8Bo6L5ZAiNxRE7lP0L4ndaNKbnPaixcoRo\n"
+"kNpPhAECgYAg7jmNlw+7VVurzR36LKKE+d6veraF5ltpJiboDb3j38RGe3982LLq\n"
+"WaBKm1gkHfXgBjkNzS4r2kyRijw0GQ9JgmWooR7BXFH30HkPNl4gFTSsrOG5zGLi\n"
+"0aexkDpXQuKsgBzqU0Wn94GZMM+RhuOYec/56JFT+8U5Tcntb26wwA==\n"
+"-----END RSA PRIVATE KEY-----\n";
+
+static const unsigned char pp[] = "IJUHZGFDXTZKHJKHGFDHZLUÖDRTFGHHJGHH";
+
+// Close files after 20 minutes
+#define ACCESS_TIMEOUT (20*60)
+
+/*
+   1 byte type: 0 allocate session, 1 log to session, rest: discard
+   8 bytes session id
+   type 0:
+      256 bytes rsa 2048 data yielding 32 byte AES session key
+   type 1:
+      16 bytes iv
+      16 bytes tag
+      rest cipher text
+
+   File name format: 2020-10-13-23-42-05-SSSSSSSSSSSSSSSS-KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK.log
+
+*/
+
+// Time helper
+static time_t now() {
+    struct timespec tp;
+    clock_gettime(CLOCK_MONOTONIC, &tp);
+    return tp.tv_sec;
+}
+
+// Constants
+enum { SESSION_ID_LENGTH = 8, AES_KEY_LENGTH = 16, GCM_IV_LENGTH = 16, GCM_TAG_LENGTH = 16, MIN_PACKET_SIZE = 40 };
+enum { FILENAME_LENGTH = 73, SIDOFFS = 20, KEYOFFS = 37 };
+
+class Session {
+public:
+    Session(uint64_t session_id, uint8_t key[AES_KEY_LENGTH], const std::string &filename) :
+            _session_id(session_id), _filename(filename) {
+        memcpy(_key, key, AES_KEY_LENGTH);
+        mbedtls_gcm_init(&_ctx);
+        mbedtls_gcm_setkey(&_ctx, MBEDTLS_CIPHER_ID_AES, _key, 8 * AES_KEY_LENGTH);
+    }
+
+    Session(uint64_t session_id, uint8_t key[AES_KEY_LENGTH]) : _session_id(session_id) {
+        memcpy(_key, key, AES_KEY_LENGTH);
+        mbedtls_gcm_init(&_ctx);
+        mbedtls_gcm_setkey(&_ctx, MBEDTLS_CIPHER_ID_AES, _key, 8 * AES_KEY_LENGTH);
+
+        // Create timestamp
+        char tprefix[32];
+        time_t t = time(NULL);
+        struct tm * jetzt = localtime(&t);
+        size_t nlen = strftime(tprefix, sizeof(tprefix), "%F-%H-%M-%S", jetzt);
+
+        // Dump key
+        char hexkey[2*AES_KEY_LENGTH + 1];
+        for (int i=0; i<AES_KEY_LENGTH; ++i)
+            sprintf(hexkey + 2 * i, "%02x", _key[i]);
+
+        // Glue together serialisation
+        char filename[FILENAME_LENGTH + 1];
+        snprintf(filename, sizeof(filename), "%s-%016" PRIx64 "-%s.log", tprefix, _session_id, hexkey);
+
+        // Touch file to save session_id and key
+        close(open(filename, O_WRONLY|O_CREAT, 0755));
+
+        _filename = std::string(filename, filename + FILENAME_LENGTH);
+    }
+
+    ~Session() {
+        mbedtls_gcm_free(&_ctx);
+    }
+
+    void write_log(const uint8_t *packet, size_t len) {
+        // First check if the packet holds enough space for session id, iv and at least one gcm block
+        if (len < GCM_IV_LENGTH + GCM_TAG_LENGTH) {
+            std::cerr << "Error: Short packet, size " << len << std::endl;
+            return;
+        }
+
+        const uint8_t *iv = packet;
+        const uint8_t *tag = packet + GCM_IV_LENGTH;
+        const uint8_t *payload = packet + GCM_IV_LENGTH + GCM_TAG_LENGTH;
+        len -= GCM_IV_LENGTH + GCM_TAG_LENGTH;
+
+        // Create output file if it doesn't exist
+        if (_fd < 0)
+            _fd = ::open(_filename.c_str(), O_WRONLY | O_APPEND | O_CREAT, 0755);
+        if (_fd < 0) {
+            std::cerr << "Error: Can't create file " << _filename << " for session " << std::hex << _session_id;
+            return;
+        }
+
+        // Prepare output scratch space
+        uint8_t *output = static_cast<uint8_t*>(alloca(len));
+
+        // This should fail on invalid input sizes
+        switch (mbedtls_gcm_auth_decrypt(&_ctx, len, iv, GCM_IV_LENGTH, (uint8_t*)&_session_id, SESSION_ID_LENGTH, tag, GCM_TAG_LENGTH, payload, output))
+        {
+            case 0:
+                write(_fd, output, len);
+                _last_access = now();
+                break;
+            case MBEDTLS_ERR_GCM_BAD_INPUT:
+                std::cerr << "Error: Invalid log data" << std::endl;
+                break;
+            case MBEDTLS_ERR_GCM_AUTH_FAILED :
+                std::cerr << "Error: Can't decrypt" << std::endl;
+                break;
+            default:
+                std::cerr << "Error: Unknown gcm error" << std::endl;
+        }
+    }
+
+    void check_timeout(time_t when) {
+        if (_last_access && _last_access < when && _fd != -1) {
+            ::close(_fd);
+            _fd = -1;
+        }
+    }
+
+private:
+    uint64_t            _session_id;
+    uint8_t             _key[AES_KEY_LENGTH];
+    int                 _fd = -1;
+    time_t              _last_access = 0;
+    std::string         _filename;
+    mbedtls_gcm_context _ctx;
+};
+
+std::map<uint64_t, std::unique_ptr<Session>> g_sessions;
+
+static uint8_t hex2nyble(char c)
+{
+    return (c>='0'&&c<='9') ? (uint8_t)(c-'0')
+        : (c>='a'&&c<='f') ? (uint8_t)(c-'a'+10)
+        : (c>='A'&&c<='F') ? (uint8_t)(c-'A'+10)
+        : 0;
+}
+
+static void import_sessions(const char *dirname) {
+    DIR * dirp = opendir(dirname);
+    if (!dirp)
+        errx(-1, "Fatal: Can't open dir %s\n", dirname);
+
+    regex_t regex;
+    if (regcomp(&regex, "^[[:digit:]]{4}-[[:digit:]][[:digit:]]-[[:digit:]][[:digit:]]-[[:digit:]][[:digit:]]-[[:digit:]][[:digit:]]-"
+                         "[[:digit:]][[:digit:]]-[[:xdigit:]]{16}-[[:xdigit:]]{32}.log$", REG_EXTENDED))
+        errx(-1, "Fatal: Can't compile re");
+
+    struct dirent * entry;
+    while ((entry = readdir(dirp)) != NULL) {
+        // We expect a very specific format
+        if (entry->d_type != DT_REG || entry->d_namlen != FILENAME_LENGTH)
+            continue;
+
+        std::string filename(entry->d_name, entry->d_name + entry->d_namlen);
+        uint64_t session_id;
+        uint8_t aeskey[AES_KEY_LENGTH];
+
+        if (regexec(&regex, filename.c_str(), (size_t) 0, NULL, 0) ||
+            sscanf(filename.c_str() + SIDOFFS, "%" SCNx64, &session_id) != 1) {
+            std::cerr << "Skipping non-re-matching file: " << filename << std::endl;
+            continue;
+        }
+
+        const char * hexkey = filename.c_str() + KEYOFFS;
+        for (int i=0; i<16; ++i)
+            aeskey[i] = (hex2nyble(hexkey[2*i]) << 4 ) | hex2nyble(hexkey[2*i+1]);
+        g_sessions[session_id] = std::make_unique<Session>(session_id, aeskey, filename);
+    }
+    closedir(dirp);
+    regfree(&regex);
+}
+
+int main() {
+    mbedtls_ctr_drbg_context ctr_drbg;
+    mbedtls_entropy_context entropy;
+    mbedtls_pk_context pk;
+    int ret = 0;
+    unsigned char result[256];
+    unsigned char input[256];
+    size_t inputlen = 0;
+
+    chdir("sessions");
+
+    mbedtls_pk_init( &pk );
+    mbedtls_entropy_init( &entropy );
+    mbedtls_ctr_drbg_init( &ctr_drbg );
+    mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy, pp, sizeof(pp));
+
+    if ((ret = mbedtls_pk_parse_key(&pk, privkey, sizeof(privkey), NULL, 0) ) != 0 )
+        errx(-1, "Fatal: mbedtls_pk_parse_key returned -0x%04x\n", -ret );
+
+    int sock = socket(AF_INET, SOCK_DGRAM, 0);
+    if (sock < 0)
+        errx(-1, "Fatal: Can not make socket\n");
+
+    struct sockaddr_in servaddr, peer;
+    servaddr.sin_family = AF_INET;
+    servaddr.sin_addr.s_addr = INADDR_ANY;
+    servaddr.sin_port = htons(PORT);
+    if (bind(sock, (const struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
+        errx(-1, "Fatal: Can't bind to port %d\n", PORT);
+
+    import_sessions(".");
+
+    time_t last_close_check = now();
+    while(1) {
+        uint8_t packet[16*1024];
+        uint8_t rsa_plain_text[AES_KEY_LENGTH];
+        size_t olen;
+        socklen_t peer_len = sizeof(peer);
+
+        ssize_t len = recvfrom(sock, packet, sizeof(packet), MSG_WAITALL, (struct sockaddr *) &peer, &peer_len);
+        if (len <= 0)
+            errx(-1, "Fatal: recvfrom yields %zd\n", len);
+
+        if (len < MIN_PACKET_SIZE) {
+            std::cerr << "Skipping short packet" << std::endl;
+            continue;
+        }
+
+        uint64_t session_id = *(uint64_t*)(packet + 1);
+        auto session = g_sessions.find(session_id);
+
+        switch(packet[0]) {
+        case 0: // Session setup
+            ret = mbedtls_pk_decrypt(&pk, packet + 1 + SESSION_ID_LENGTH, len - 1 - SESSION_ID_LENGTH,
+                                     rsa_plain_text, &olen, sizeof(rsa_plain_text), mbedtls_ctr_drbg_random, &ctr_drbg);
+            if (ret < 0) {
+                std::cerr << "Error: Failed to decrypt key (error " << -ret << ") for session " << std::hex << session_id;
+                break;
+            }
+
+            if (session == g_sessions.end())
+                g_sessions[session_id] = std::make_unique<Session>(session_id, rsa_plain_text);
+            break;
+        case 1:
+            if (session != g_sessions.end())
+                session->second->write_log(packet + 1 + SESSION_ID_LENGTH, len - 1 - SESSION_ID_LENGTH);
+            else
+                std::cerr << "Error: Can't log to unknown session " << std::hex << session_id << std::endl;
+            break;
+        default:
+            break;
+        }
+
+        time_t jetzt = now();
+        if (jetzt > last_close_check + 60) {
+            for (auto &&session: g_sessions)
+                session.second->check_timeout(jetzt - ACCESS_TIMEOUT);
+            last_close_check = jetzt;
+        }
+    }
+}