new: added qc_decrypt utility

4 files changed, 160 insertions, 0 deletions

diff --git a/qc_decrypt/.gitignore b/qc_decrypt/.gitignore
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+qc_decrypt
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diff --git a/qc_decrypt/Makefile b/qc_decrypt/Makefile
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+++ b/qc_decrypt/Makefile
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+all: 
+	@gcc -I/opt/homebrew/opt/openssl/include -L/opt/homebrew/opt/openssl/lib -lcrypto qc_decrypt.c -o qc_decrypt
+
+clean:
+	@rm -rf qc_decrypt
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diff --git a/qc_decrypt/README.md b/qc_decrypt/README.md
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+NeuralDSP QuadCortex file decryptor.
+
+Compile with `make` (requires gcc and openssl-dev installed), then pass the serial number found in `/etc/qc_sn` as command line argument:
+
+```sh
+./qc_decrypt QA00XXXXX /path/to/encrypted.json/cns/ldr/... > decrypted.dat
+```
+
+## License
+
+This tool was made with ♥  by [Simone Margaritelli](https://www.evilsocket.net/) and it is released under the GPL 3 license.
diff --git a/qc_decrypt/qc_decrypt.c b/qc_decrypt/qc_decrypt.c
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+/*
+ * Copyright (c) 2023 Simone 'evilsocket' Margaritelli - [email protected].
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * 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 <openssl/conf.h>
+#include <openssl/evp.h>
+#include <openssl/err.h>
+#include <string.h>
+#include <stdio.h>
+
+// as seen in /usr/lib/libzc.so / SetupKeys
+static unsigned char KEY_MATERIAL[] = {
+    0x13, 0x27, 0x3f, 0x42,
+    0xa5, 0xb6, 0x79, 0xe8,
+    0x20, 0x31, 0xc4, 0xf5,
+    0x16, 0x17, 0x88, 0x2f,
+    0x43, 0xa4, 0x55, 0x69,
+    0x77, 0xb8, 0xe2, 0x83,
+    0x04, 0x05, 0x60, 0x70,
+    0x80, 0x02, 0x03, 0x04,
+    0x50, 0x6a, 0x7c, 0x8a,
+    0x02, 0x30, 0x40, 0x51,
+    0x6a, 0x7d, 0x8d, 0x22,
+    0x33, 0x44, 0x59, 0x66,
+    0x71, 0x08, 0x02, 0x03,
+    0x43, 0x05, 0x67, 0x7a,
+    0x8f};
+
+int main(int argc, char **argv)
+{
+    if (argc != 3)
+    {
+        printf("Usage: %s <serial number> <encrypted file>\n", argv[0]);
+        return 1;
+    }
+
+    char *serialNumber = argv[1],
+         *inputFileName = argv[2];
+
+    unsigned long serialSize = strlen(serialNumber);
+    if (serialSize != 9)
+    {
+        printf("the serial number must be 9 characters long.\n");
+        return 1;
+    }
+
+    // concatenate the hardcoded key material with the serial number from /etc/qc_sn
+    unsigned long key_material_size = sizeof(KEY_MATERIAL) / sizeof(KEY_MATERIAL[0]);
+    unsigned char *key_material = (unsigned char *)malloc(key_material_size + serialSize);
+
+    memcpy(key_material, KEY_MATERIAL, key_material_size);
+    memcpy(key_material + key_material_size, serialNumber, serialSize);
+
+    key_material_size += serialSize;
+
+    // derive the actual key and iv from it
+    unsigned char key[32] = {0};
+    unsigned char iv[32] = {0};
+
+    int iterations = 10;
+    const EVP_CIPHER *pCipher = EVP_aes_128_ctr();
+    const EVP_MD *pDigest = EVP_sha1();
+
+    int derivedKeySize = EVP_BytesToKey(
+        pCipher,
+        pDigest,
+        NULL, // no salt
+        key_material,
+        key_material_size,
+        iterations,
+        key,
+        iv);
+
+    if (derivedKeySize != 16)
+    {
+        printf("wrong derived key size: %d\n", derivedKeySize);
+        return 1;
+    }
+
+    // read the encrypted file
+    FILE *fp = fopen(inputFileName, "rb");
+    if (!fp)
+    {
+        printf("can't open %s\n", inputFileName);
+        return 1;
+    }
+
+    fseek(fp, 0, SEEK_END);
+    long input_size = ftell(fp);
+    fseek(fp, 0, SEEK_SET);
+
+    int ret, final_size, outlen;
+    unsigned char *input = (unsigned char *)malloc(input_size),
+                  *plaintext = (unsigned char *)malloc(input_size);
+
+    long read = fread(input, 1, input_size, fp);
+
+    fclose(fp);
+
+    // decrypt it
+    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+
+    ret = EVP_DecryptInit_ex(ctx, pCipher, NULL, key, iv);
+    if (ret != 1)
+    {
+        printf("EVP_DecryptInit_ex failed: %d\n", ret);
+        return 1;
+    }
+
+    ret = EVP_DecryptUpdate(ctx, plaintext, &outlen, input, input_size);
+    if (ret != 1)
+    {
+        printf("EVP_DecryptUpdate failed: %d\n", ret);
+        return 1;
+    }
+
+    ret = EVP_DecryptFinal(ctx, &plaintext[outlen], &final_size);
+    if (ret != 1)
+    {
+        printf("EVP_DecryptFinal failed: %d\n", ret);
+        return 1;
+    }
+
+    // print it
+    for (int i = 0; i < outlen; i++)
+    {
+        printf("%c", plaintext[i]);
+    }
+    printf("\n");
+
+    return 0;
+}
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