soutade/libgourou
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Fix over encrypted RSA key decryption algorithm

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This commit is contained in:
Grégory Soutadé 2022-12-21 20:15:11 +01:00
parent 7878f91cdd
commit afab1c0012
2 changed files with 12 additions and 18 deletions
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2
include/libgourou.h
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@ -231,7 +231,7 @@ namespace gourou
void buildSignInRequest(pugi::xml_document& signInRequest, const std::string& adobeID, const std::string& adobePassword, const std::string& authenticationCertificate);
void fetchLicenseServiceCertificate(const std::string& licenseURL,
const std::string& operatorURL);
std::string encryptedKeyFirstPass(pugi::xml_document& rightsDoc, const std::string& encryptedKey, const std::string& keyType, ITEM_TYPE type);
std::string encryptedKeyFirstPass(pugi::xml_document& rightsDoc, const std::string& encryptedKey, const std::string& keyType);
void decryptADEPTKey(const std::string& encryptedKey, unsigned char* decryptedKey);
void removeEPubDRM(const std::string& filenameIn, const std::string& filenameOut, const unsigned char* encryptionKey, unsigned encryptionKeySize);
void generatePDFObjectKey(int version,

28
src/libgourou.cpp
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@ -963,13 +963,13 @@ namespace gourou
/**
* RSA Key can be over encrypted with AES128-CBC if keyType attribute is set
* For EPUB, Key = SHA256(keyType)[14:22] || SHA256(keyType)[7:13]
* For PDF, Key = SHA256(keyType)[6:19] || SHA256(keyType)[3:6]
* remainder = keyType % 16
* Key = SHA256(keyType)[remainder*2:remainder*2+(16-remainder)] || SHA256(keyType)[16-remainder:16]
* IV = DeviceID ^ FulfillmentId ^ VoucherId
*
* @return Base64 encoded decrypted key
*/
std::string DRMProcessor::encryptedKeyFirstPass(pugi::xml_document& rightsDoc, const std::string& encryptedKey, const std::string& keyType, ITEM_TYPE type)
std::string DRMProcessor::encryptedKeyFirstPass(pugi::xml_document& rightsDoc, const std::string& encryptedKey, const std::string& keyType)
{
unsigned char digest[32], key[16], iv[16];
unsigned int dataOutLength;
@ -979,18 +979,12 @@ namespace gourou
dumpBuffer(gourou::LG_LOG_DEBUG, "SHA of KeyType : ", digest, sizeof(digest));
switch(type)
{
case EPUB:
memcpy(key, &digest[14], 9);
memcpy(&key[9], &digest[7], 7);
break;
case PDF:
memcpy(key, &digest[6], 13);
memcpy(&key[13], &digest[3], 3);
break;
}
long nonce = std::stol(keyType);
int remainder = nonce % 16;
memcpy(key, &digest[remainder*2], 16-remainder);
memcpy(&key[16-remainder], &digest[remainder], remainder);
id = extractTextElem(rightsDoc, "/adept:rights/licenseToken/device");
if (id == "")
EXCEPTION(DRM_ERR_ENCRYPTION_KEY_FP, "Device id not found in rights.xml");
@ -1021,7 +1015,7 @@ namespace gourou
dumpBuffer(gourou::LG_LOG_DEBUG, "First pass IV : ", iv, sizeof(iv));
unsigned char* clearRSAKey = new unsigned char[arrayEncryptedKey.size()];
client->decrypt(CryptoInterface::ALGO_AES, CryptoInterface::CHAIN_CBC,
(const unsigned char*)key, (unsigned int)sizeof(key),
(const unsigned char*)iv, (unsigned int)sizeof(iv),
@ -1067,7 +1061,7 @@ namespace gourou
std::string keyType = extractTextAttribute(rightsDoc, "/adept:rights/licenseToken/encryptedKey", "keyType", false);
if (keyType != "")
encryptedKey = encryptedKeyFirstPass(rightsDoc, encryptedKey, keyType, EPUB);
encryptedKey = encryptedKeyFirstPass(rightsDoc, encryptedKey, keyType);
decryptADEPTKey(encryptedKey, decryptedKey);
@ -1262,7 +1256,7 @@ namespace gourou
std::string keyType = extractTextAttribute(rightsDoc, "/adept:rights/licenseToken/encryptedKey", "keyType", false);
if (keyType != "")
encryptedKey = encryptedKeyFirstPass(rightsDoc, encryptedKey, keyType, PDF);
encryptedKey = encryptedKeyFirstPass(rightsDoc, encryptedKey, keyType);
decryptADEPTKey(encryptedKey, decryptedKey);