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https://github.com/moparisthebest/ImageDownloader
synced 2024-11-26 19:22:16 -05:00
Support new 12-byte IV format and legacy 16-byte IV format
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@ -1,7 +1,9 @@
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# ImageDownloader
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When [Conversations](https://conversations.im) uploads an encrypted image with [XEP-0363: HTTP Upload](http://xmpp.org/extensions/xep-0363.html) it appends the encryption key as an anchor to the URL.
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The anchor is made of 96 characters which represent 48 bytes in HEX. The first 16 bytes are the IV the last 32 bytes are the key.
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There are now [2 formats for anchors](https://github.com/siacs/Conversations/issues/2578).
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*LEGACY FORMAT*: The anchor is made of 96 characters which represent 48 bytes in HEX. The first 16 bytes are the IV the last 32 bytes are the key.
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*CURRENT FORMAT*: The anchor is made of 88 characters which represent 44 bytes in HEX. The first 12 bytes are the IV the last 32 bytes are the key.
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The encryption mode is ```aes-256-gcm```. The authentication tag of 16 bytes is appended to the file.
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35
aesgcm.c
35
aesgcm.c
@ -3,13 +3,14 @@
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#include <unistd.h>
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#include <openssl/evp.h>
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#define TAG_IV_LENGTH 16
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#define TAG_LENGTH 16
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#define BYTES_PER_READ 32 * 1024 // 32kb
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#define INITIAL_BUFFER_SIZE 256 * 1024 // 256kb, must be at least 2*BYTES_PER_READ
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void hex2string(char *src, unsigned char **dst_p)
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unsigned int hex2string(char *src, unsigned char **dst_p)
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{
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*dst_p = malloc(strlen(src)/2);
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unsigned int byte_length = strlen(src)/2;
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*dst_p = malloc(byte_length);
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unsigned char *dst = *dst_p;
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unsigned char *end = dst + (strlen(src)/2);
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unsigned int u;
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@ -18,6 +19,7 @@ void hex2string(char *src, unsigned char **dst_p)
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*dst++ = u;
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src += 2;
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}
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return byte_length;
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}
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int main(int argc, char **argv)
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@ -35,7 +37,16 @@ int main(int argc, char **argv)
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if (argc > 2 && strcmp("enc", argv[2]) == 0)
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decrypt = 0;
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hex2string(argv[1], &gcm_ivkey);
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unsigned int byte_length = hex2string(argv[1], &gcm_ivkey);
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unsigned int iv_length;
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if(byte_length == 48) {
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iv_length = 16;
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} else if(byte_length == 44) {
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iv_length = 12;
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} else {
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fprintf(stderr, "Invalid key length %d only 44 or 48 bytes supported\n", byte_length);
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return 1;
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}
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gcm_ct = malloc(total_size);
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@ -53,9 +64,9 @@ int main(int argc, char **argv)
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}
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if(decrypt)
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actual_size -= TAG_IV_LENGTH;
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actual_size -= TAG_LENGTH;
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gcm_pt = malloc(decrypt ? actual_size : (actual_size + TAG_IV_LENGTH));
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gcm_pt = malloc(decrypt ? actual_size : (actual_size + TAG_LENGTH));
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EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
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@ -66,14 +77,14 @@ int main(int argc, char **argv)
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EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);
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/* Set IV length, omit for 96 bits */
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EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, TAG_IV_LENGTH, NULL);
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EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, iv_length, NULL);
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if(decrypt) {
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/* Specify key and IV */
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EVP_DecryptInit_ex(ctx, NULL, NULL, gcm_ivkey + TAG_IV_LENGTH, gcm_ivkey);
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EVP_DecryptInit_ex(ctx, NULL, NULL, gcm_ivkey + iv_length, gcm_ivkey);
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/* Set expected tag value. */
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EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, TAG_IV_LENGTH, gcm_ct + actual_size);
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EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, TAG_LENGTH, gcm_ct + actual_size);
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/* Decrypt plaintext */
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EVP_DecryptUpdate(ctx, gcm_pt, &outlen, gcm_ct, actual_size);
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@ -82,7 +93,7 @@ int main(int argc, char **argv)
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rv = EVP_DecryptFinal_ex(ctx, gcm_pt, &final_outlen);
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} else {
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/* Specify key and IV */
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EVP_EncryptInit_ex(ctx, NULL, NULL, gcm_ivkey + TAG_IV_LENGTH, gcm_ivkey);
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EVP_EncryptInit_ex(ctx, NULL, NULL, gcm_ivkey + iv_length, gcm_ivkey);
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/* Encrypt plaintext */
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EVP_EncryptUpdate(ctx, gcm_pt, &outlen, gcm_ct, actual_size);
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@ -91,7 +102,7 @@ int main(int argc, char **argv)
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rv = EVP_EncryptFinal_ex(ctx, gcm_pt, &final_outlen);
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/* Get expected tag value. */
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EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, TAG_IV_LENGTH, gcm_pt + actual_size);
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EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, TAG_LENGTH, gcm_pt + actual_size);
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}
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EVP_CIPHER_CTX_free(ctx);
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@ -100,7 +111,7 @@ int main(int argc, char **argv)
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if (rv > 0) {
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// success!
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fwrite(gcm_pt, 1, decrypt ? outlen : (outlen + TAG_IV_LENGTH), stdout);
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fwrite(gcm_pt, 1, decrypt ? outlen : (outlen + TAG_LENGTH), stdout);
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free(gcm_pt);
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return 0;
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} else {
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