4 files changed, 418 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..631717d
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,10 @@
+all: sender receiver
+
+sender: sender.c
+        $(CC) -o sender sender.c -lmbedtls -lmbedcrypto
+
+receiver: receiver.c
+        $(CC) -o receiver receiver.c -lmbedtls -lmbedcrypto
+
+clean:
+        rm -f sender receiver
diff --git a/receiver.c b/receiver.c
new file mode 100644
index 0000000..b7171d9
--- /dev/null
+++ b/receiver.c
@@ -0,0 +1,298 @@
+#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"
+
+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";
+
+/*
+   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
+
+*/
+
+enum { SESSION_ID_LENGTH = 8, AES_KEY_LENGTH = 16, GCM_IV_LENGTH = 16, GCM_TAG_LENGTH = 16 };
+typedef struct {
+    uint8_t session_id[SESSION_ID_LENGTH];
+    uint8_t key[AES_KEY_LENGTH];
+    int     fd; // or -1 if not existing
+    time_t  last_access;
+    char    file_name[80];
+} SESSION;
+static SESSION *g_sessions = 0;
+static size_t g_session_count = 0;
+
+int session_compare(const void *a, const void *b) { return memcmp(a, b, 8); }
+
+enum { SIDOFFS = 20, KEYOFFS = 37, };
+
+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);
+
+    free(g_sessions);
+    g_session_count = 0;
+
+    size_t allocated = 1024;
+    g_sessions = malloc(allocated * sizeof(SESSION));
+    if (!g_sessions)
+        errx(-1, "Fatal: Out of memory");
+
+    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 != 73) {
+            fprintf(stderr, "Skipping wrong length file: %*s\n", entry->d_namlen, entry->d_name);
+            continue;
+        }
+
+        SESSION *ns = g_sessions + g_session_count;
+
+        memcpy(ns->file_name, entry->d_name, entry->d_namlen);
+        ns->file_name[entry->d_namlen] = 0;
+        ns->fd = -1;
+        ns->last_access = 0;
+
+        if (regexec(&regex, ns->file_name, (size_t) 0, NULL, 0)) {
+            fprintf(stderr, "Skipping non-re-matching file: %s\n", ns->file_name);
+            continue;
+        }
+
+        if (sscanf(ns->file_name + SIDOFFS, "%" SCNx64, (uint64_t*)&ns->session_id) != 1) {
+            fprintf(stderr, "Skipping non-parsable file: %s\n", ns->file_name);
+            continue;
+        }
+        const char * hexkey = ns->file_name + KEYOFFS;
+        for (int i=0; i<16; ++i)
+            ns->key[i] = (hex2nyble(hexkey[2*i]) << 4 ) | hex2nyble(hexkey[2*i+1]);
+
+        // Need more memory?
+        if (++g_session_count > allocated) {
+            allocated += 1024;
+            g_sessions = realloc(g_sessions, allocated * sizeof(SESSION));
+            if (!g_sessions)
+                errx(-1, "Fatal: Out of memory");
+        }
+    }
+    closedir(dirp);
+    regfree(&regex);
+
+    qsort(g_sessions, g_session_count, sizeof(SESSION), session_compare);
+}
+
+static void add_session(uint8_t *session_id, uint8_t aes_key[AES_KEY_LENGTH]) {
+    // We don't overwrite existing sessions
+    if (bsearch(session_id, g_sessions, g_session_count, sizeof(SESSION), session_compare))
+        return;
+
+    SESSION * sessions_realloc = realloc(g_sessions, sizeof(SESSION) * (1 + g_session_count));
+
+    if (!sessions_realloc)
+        errx(-1, "Fatal: Out of memory");
+
+    g_sessions = sessions_realloc;
+    SESSION * new_session = &g_sessions[g_session_count];
+    g_session_count++;
+
+    memcpy(new_session->session_id, session_id, SESSION_ID_LENGTH);
+    memcpy(new_session->key, aes_key, AES_KEY_LENGTH);
+    new_session->fd = -1;
+    new_session->last_access = 0;
+
+    time_t t = time(NULL);
+    struct tm * jetzt = localtime(&t);
+    char tprefix[32], hexkey[2*AES_KEY_LENGTH + 1];
+    size_t nlen = strftime(tprefix, sizeof(tprefix), "%F-%H-%M-%S", jetzt);
+    for (int i=0; i<AES_KEY_LENGTH; ++i)
+        sprintf(hexkey + 2 * i, "%02x", aes_key[i]);
+    int off = snprintf(new_session->file_name, sizeof(new_session->file_name),
+                        "%s-%" PRIx64 "-%s.log", tprefix, *(uint64_t*)session_id, hexkey);
+    int fd = open("new_session->file_name", O_RDWR|O_CREAT, 0755);
+    close(fd);
+
+    mergesort(g_sessions, g_session_count, sizeof(SESSION), session_compare);
+}
+
+static time_t now() {
+    struct timespec tp;
+    clock_gettime(CLOCK_MONOTONIC, &tp);
+    return tp.tv_sec;
+}
+
+static void log_to_session(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 < SESSION_ID_LENGTH + GCM_IV_LENGTH + GCM_TAG_LENGTH) {
+        fprintf(stderr, "Error: Short packet, size %zd\n", len);
+        return;
+    }
+
+    const uint8_t *session_id = packet;
+    const uint8_t *iv = packet + SESSION_ID_LENGTH;
+    const uint8_t *tag = packet + SESSION_ID_LENGTH + GCM_IV_LENGTH;
+    packet += SESSION_ID_LENGTH + GCM_IV_LENGTH + GCM_TAG_LENGTH;
+    len -= SESSION_ID_LENGTH + GCM_IV_LENGTH + GCM_TAG_LENGTH;
+
+    SESSION * s = bsearch(session_id, g_sessions, g_session_count, sizeof(SESSION), session_compare);
+    if (!s) {
+        fprintf(stderr, "Error: Can't log to unknown session 0x%" PRIx64 "\n", *(uint64_t*)session_id);
+        return;
+    }
+
+    // Create output file if it doesn't exist
+    if (s->fd < 0)
+        s->fd = open(s->file_name, O_WRONLY | O_APPEND | O_CREAT, 0755);
+    if (s->fd < 0) {
+        fprintf(stderr, "Error: Can't create file %s for session 0x%" PRIx64 "\n", s->file_name, *(uint64_t*)packet);
+        return;
+    }
+
+    // Now decrypt
+    mbedtls_gcm_context ctx;
+    mbedtls_gcm_init(&ctx);
+    mbedtls_gcm_setkey(&ctx, MBEDTLS_CIPHER_ID_AES, s->key, 8 * AES_KEY_LENGTH);
+
+    // Prepare output scratch space
+    uint8_t *output = alloca(len);
+
+    // This should fail on invalid input sizes
+    switch(mbedtls_gcm_auth_decrypt(&ctx, len, iv, GCM_IV_LENGTH, session_id, SESSION_ID_LENGTH, tag, GCM_TAG_LENGTH, packet, output))
+    {
+        case 0:
+            write(s->fd, output, len);
+            s->last_access = now();
+            break;
+        case MBEDTLS_ERR_GCM_BAD_INPUT:
+            fprintf(stderr, "Error: Invalid log data\n");
+            break;
+        case MBEDTLS_ERR_GCM_AUTH_FAILED :
+            fprintf(stderr, "Error: Can't decrypt\n");
+            break;
+        default:
+            fprintf(stderr, "Error: Unknown gcm error\n");
+    }
+
+    mbedtls_gcm_free(&ctx);
+}
+
+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(".");
+
+    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);
+        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)
+                fprintf(stderr, "Error: Failed to decrypt key (error %d) for session 0x%" PRIx64 "\n", -ret, *(uint64_t *)(packet + 1));
+            else
+                add_session(packet + 1, rsa_plain_text);
+            break;
+        case 1:
+            log_to_session(packet + 1, len - 1);
+            break;
+        default:
+            break;
+        }
+    }
+}
diff --git a/sender.c b/sender.c
new file mode 100644
index 0000000..3469735
--- /dev/null
+++ b/sender.c
@@ -0,0 +1,110 @@
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <string.h>
+#include <err.h>
+#include <inttypes.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+
+#include <mbedtls/pk.h>
+#include <mbedtls/entropy.h>
+#include "mbedtls/ctr_drbg.h"
+#include "mbedtls/gcm.h"
+
+const unsigned short PORT = 58132;
+
+static const unsigned char pubkey[] =
+"-----BEGIN PUBLIC KEY-----\n"
+"MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAwWlNmLHOOzZpdrfp+EAA\n"
+"Nwqab0FhQwCyZ/u+ySBW5XxPf6mobySvtJrLdsWzdwnup/UfwZiEhJk/4wpD4Qf/\n"
+"2+syuJi3Rf7L+Jfh//Qf9uXAS80+LYad7dW0c1r5nt+F9Can5fBn7futnd8n672T\n"
+"+y8QpHRwX9GtaILvYQe5GQac8cfq2rGUd5iYj5KSdcaIZnJ4YgnjLHg2PMbtEJwq\n"
+"cV+2oAkcOPzTAJoNE7XjLZTwXmLlFgL/2cN4uJZBDnwv3RZSAhpdYF4KOJmE2GFs\n"
+"2jdvRUrYO7WSl8fM16vRH4vz5MNNcaprg2MlXheVTPQa+WMdcz7dyQx8s9kRVPPU\n"
+"SwIDAQAB \n"
+"-----END PUBLIC KEY----- \n";
+
+static const unsigned char pp[] = "IJUHZGFDXTZKHJKHGFDHZLUÖDRTFGHHJGHH";
+
+enum { SESSION_ID_LENGTH = 8, AES_KEY_LENGTH = 16, GCM_IV_LENGTH = 16, GCM_TAG_LENGTH = 16 };
+static uint8_t session_id[8] = { 0xef, 0xcd, 0xab, 0x89, 0x67, 0x45, 0x23, 0x01 };
+static uint8_t aes_key[16] = { 0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef, 0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef };
+
+void send_udp(int sock, mbedtls_ctr_drbg_context *ctr_drbg, const uint8_t *text, size_t len) {
+    uint8_t iv[GCM_IV_LENGTH];
+    mbedtls_ctr_drbg_random(ctr_drbg, iv, sizeof(GCM_IV_LENGTH));
+
+    const size_t total_length = 1 + SESSION_ID_LENGTH + GCM_IV_LENGTH + GCM_TAG_LENGTH + len;
+    uint8_t *output = alloca(total_length);
+    output[0] = 1;
+    memcpy(output + 1, session_id, SESSION_ID_LENGTH);
+    memcpy(output + 1 + SESSION_ID_LENGTH, iv, GCM_IV_LENGTH);
+
+    mbedtls_gcm_context ctx;
+    mbedtls_gcm_init(&ctx);
+    mbedtls_gcm_setkey(&ctx, MBEDTLS_CIPHER_ID_AES, aes_key, 8 * AES_KEY_LENGTH);
+
+    if (!mbedtls_gcm_crypt_and_tag(&ctx, MBEDTLS_GCM_ENCRYPT, len, iv, GCM_IV_LENGTH, session_id, SESSION_ID_LENGTH,
+                                  text, output + 1 + SESSION_ID_LENGTH + GCM_IV_LENGTH + GCM_TAG_LENGTH, GCM_TAG_LENGTH,
+                                  output + 1 + SESSION_ID_LENGTH + GCM_IV_LENGTH)) {
+        struct sockaddr_in to;
+        memset(&to, 0, sizeof(to));
+        to.sin_family      = AF_INET;
+        to.sin_addr.s_addr = inet_addr("127.0.0.1");
+        to.sin_port        = htons(PORT);
+
+        sendto(sock, output, total_length, 0, (struct sockaddr*)&to, sizeof(to));
+    }
+
+    mbedtls_gcm_free(&ctx);
+}
+
+void new_session(int sock, mbedtls_ctr_drbg_context *ctr_drbg) {
+    mbedtls_ctr_drbg_random(ctr_drbg, session_id, sizeof(session_id));
+    mbedtls_ctr_drbg_random(ctr_drbg, aes_key, sizeof(aes_key));
+
+    unsigned char output[512];
+    output[0] = 0;
+    memcpy(output + 1, session_id, SESSION_ID_LENGTH);
+
+    mbedtls_pk_context pk;
+    mbedtls_pk_init(&pk);
+    int ret = 0;
+    if ((ret = mbedtls_pk_parse_public_key(&pk, pubkey, sizeof(pubkey)) ) != 0 )
+        errx(-1, "mbedtls_pk_parse_public_keyfile returned -0x%04x\n", -ret );
+
+    size_t olen = 0;
+    if ((ret = mbedtls_pk_encrypt(&pk, aes_key, AES_KEY_LENGTH, output + 1 + SESSION_ID_LENGTH, &olen,
+                                  sizeof(output) - 1 - SESSION_ID_LENGTH, mbedtls_ctr_drbg_random, ctr_drbg)) != 0)
+        errx(-1, "mbedtls_pk_encrypt returned -0x%04x\n", -ret );
+
+    mbedtls_pk_free(&pk);
+
+    struct sockaddr_in to;
+    memset(&to, 0, sizeof(to));
+    to.sin_family      = AF_INET;
+    to.sin_addr.s_addr = inet_addr("127.0.0.1");
+    to.sin_port        = htons(PORT);
+
+    sendto(sock, output, olen + 1 + SESSION_ID_LENGTH, 0, (struct sockaddr*)&to, sizeof(to));
+}
+
+int main() {
+    mbedtls_ctr_drbg_context ctr_drbg;
+    mbedtls_entropy_context entropy;
+
+    mbedtls_entropy_init(&entropy);
+    mbedtls_ctr_drbg_init(&ctr_drbg);
+    mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy, pp, sizeof(pp));
+
+    int sock = socket(AF_INET, SOCK_DGRAM, 0);
+
+    new_session(sock, &ctr_drbg);
+
+    sleep(3);
+
+    const unsigned char *logline = (const unsigned char*)"Juchuuu, es klappt!\n";
+    send_udp(sock, &ctr_drbg, logline, strlen((char*)logline));
+
+    close(sock);
+}
diff --git a/sessions/.empty b/sessions/.empty
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/sessions/.empty