源码过程分析:
第一，chrome创建一个url请求的时候，如何获取cookie，源码文件名network_context.cc，
在MakeURLRequestContext方法中调用:
crypto_delegate = cookie_config::GetCookieCryptoDelegate();
cookie_config namespace下的GetCookieCryptoDelegate方法,
接着看道头文件中 #include "components/cookie_config/cookie_store_util.h"
猜测GetCookieCryptoDelegate在cookie_store_util.h中定义,
查看其源代码，如下：
namespace net {
class CookieCryptoDelegate;
} // namespace net
namespace cookie_config {
// Factory method for returning a CookieCryptoDelegate if one is appropriate for
// this platform. The object returned is a LazyInstance. Ownership is not
// transferred.
net::CookieCryptoDelegate* GetCookieCryptoDelegate();
} // namespace cookie_config
可以看到，是有这个方法，接着再其对应cookie_store_util.cc文件中，查看其实现方式：
namespace cookie_config {
#if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
namespace {
// Use the operating system's mechanisms to encrypt cookies before writing
// them to persistent store. Currently this only is done with desktop OS's
// because ChromeOS and Android already protect the entire profile contents.
class CookieOSCryptoDelegate : public net::CookieCryptoDelegate {
public:
bool ShouldEncrypt() override;
bool EncryptString(const std::string& plaintext,
std::string* ciphertext) override;
bool DecryptString(const std::string& ciphertext,
std::string* plaintext) override;
};
bool CookieOSCryptoDelegate::ShouldEncrypt() {
#if defined(OS_IOS)
// Cookie encryption is not necessary on iOS, due to OS-protected storage.
// However, due to https://codereview.chromium.org/135183021/, cookies were
// accidentally encrypted. In order to allow these cookies to still be used,a
// a CookieCryptoDelegate is provided that can decrypt existing cookies.
// However, new cookies will not be encrypted. The alternatives considered
// were not supplying a delegate at all (thus invalidating all existing
// encrypted cookies) or in migrating all cookies at once, which may impose
// startup costs. Eventually, all cookies will get migrated as they are
// rewritten.
return false;
#else
return true;
#endif
}
bool CookieOSCryptoDelegate::EncryptString(const std::string& plaintext,
std::string* ciphertext) {
return OSCrypt::EncryptString(plaintext, ciphertext);
}
bool CookieOSCryptoDelegate::DecryptString(const std::string& ciphertext,
std::string* plaintext) {
return OSCrypt::DecryptString(ciphertext, plaintext);
}
// Using a LazyInstance is safe here because this class is stateless and
// requires 0 initialization.
base::LazyInstance<CookieOSCryptoDelegate>::DestructorAtExit
g_cookie_crypto_delegate = LAZY_INSTANCE_INITIALIZER;
} // namespace
net::CookieCryptoDelegate* GetCookieCryptoDelegate() {
return g_cookie_crypto_delegate.Pointer();
}
#else // defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
net::CookieCryptoDelegate* GetCookieCryptoDelegate() {
return NULL;
}
#endif // defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
} // namespace cookie_config
可以看到里边定义了，cookie的加密和解密方法以及各种不同平台是否需要加密,
其中ios平台不需要加密,加密解密时调用了OSCrypt::DecryptString和OSCrypt::EncryptString方法，
再查看头文件#include "components/os_crypt/os_crypt.h",
找os_crypt，发现在不同的系统平台下，有不同的实现方式，
本文重点分析windows平台下的实现os_crypt_win.cc,源码如下：
#include "components/os_crypt/os_crypt.h"
#include <windows.h>
#include "base/strings/utf_string_conversions.h"
#include "base/win/wincrypt_shim.h"
bool OSCrypt::EncryptString16(const base::string16& plaintext,
std::string* ciphertext) {
return EncryptString(base::UTF16ToUTF8(plaintext), ciphertext);
}
bool OSCrypt::DecryptString16(const std::string& ciphertext,
base::string16* plaintext) {
std::string utf8;
if (!DecryptString(ciphertext, &utf8))
return false;
*plaintext = base::UTF8ToUTF16(utf8);
return true;
}
bool OSCrypt::EncryptString(const std::string& plaintext,
std::string* ciphertext) {
DATA_BLOB input;
input.pbData = const_cast<BYTE*>(
reinterpret_cast<const BYTE*>(plaintext.data()));
input.cbData = static_cast<DWORD>(plaintext.length());
DATA_BLOB output;
BOOL result =
CryptProtectData(&input, L"", nullptr, nullptr, nullptr, 0, &output);
if (!result) {
PLOG(ERROR) << "Failed to encrypt";
return false;
}
// this does a copy
ciphertext->assign(reinterpret_cast<std::string::value_type*>(output.pbData),
output.cbData);
LocalFree(output.pbData);
return true;
}
bool OSCrypt::DecryptString(const std::string& ciphertext,
std::string* plaintext) {
DATA_BLOB input;
input.pbData = const_cast<BYTE*>(
reinterpret_cast<const BYTE*>(ciphertext.data()));
input.cbData = static_cast<DWORD>(ciphertext.length());
DATA_BLOB output;
BOOL result = CryptUnprotectData(&input, nullptr, nullptr, nullptr, nullptr,
0, &output);
if (!result) {
PLOG(ERROR) << "Failed to decrypt";
return false;
}
plaintext->assign(reinterpret_cast<char*>(output.pbData), output.cbData);
LocalFree(output.pbData);
return true;
}
里边定义了cookie最终使用的加密和解密的方法，才用了windows加密解密API CryptProtectData
和 CryptUnprotectData这2个方法，
至此chromium cookie加密解密方法分析完成。
第二：cookie保存过程分析
再第一步的分析中,network_context.cc文件中，
在MakeURLRequestContext方法中调用:
crypto_delegate = cookie_config::GetCookieCryptoDelegate()
;创建了一个加密解密的对象，后面是如何传递到cookie读取保存时用于加密解密呢，再这个文件中继续向下分析，可以看到
>>scoped_refptrnet::SQLitePersistentCookieStore sqlite_store(
>>>> new net::SQLitePersistentCookieStore(
>>>>>> params_->cookie_path.value(), client_task_runner,
>>>>>> background_task_runner, params_->restore_old_session_cookies,
>>>> crypto_delegate));
将crypto_delegate传到了net::SQLitePersistentCookieStore
这个对象中，这个对象的源文件是sqlite_persistent_cookie_store.cc文件，可以看到保存过程如下：
>>case PendingOperation::COOKIE_ADD:
>>>>add_smt.Reset(true);
>>>>add_smt.BindInt64(0, po->cc().CreationDate().ToInternalValue());
>>>>add_smt.BindString(1, po->cc().Domain());
>>>>add_smt.BindString(2, po->cc().Name());
>>>>if (crypto_ && crypto_->ShouldEncrypt()) {
>>>>>>std::string encrypted_value;
>>>>>>if (!crypto_->EncryptString(po->cc().Value(), &encrypted_value)) {
>>>>>>>>DLOG(WARNING) << "Could not encrypt a cookie, skipping add.";
>>>>>>>>RecordCookieCommitProblem(COOKIE_COMMIT_PROBLEM_ENCRYPT_FAILED);
>>>>>>>>trouble = true;
>>>>>>>>continue;
>>>>>>}
>>>>>>add_smt.BindCString(3, ""); // value
>>>>>>>>// BindBlob() immediately makes an internal copy of the data.
>>>>>>>>add_smt.BindBlob(4, encrypted_value.data(), static_cast(encrypted_value.length()));
>>>>>>} else {
>>>>>>>>add_smt.BindString(3, po->cc().Value());
>>>>>>>>add_smt.BindBlob(4, "", 0); // encrypted_value
>>>>>>}
>>>>>>add_smt.BindString(5, po->cc().Path());
>>>>>>add_smt.BindInt64(6, po->cc().ExpiryDate().ToInternalValue());
>>>>>>add_smt.BindInt(7, po->cc().IsSecure());
>>>>>>add_smt.BindInt(8, po->cc().IsHttpOnly());
>>>>>>add_smt.BindInt( 9, CookieSameSiteToDBCookieSameSite(po->cc().SameSite()));
>>>>>>add_smt.BindInt64(10, po->cc().LastAccessDate().ToInternalValue());
>>>>>> add_smt.BindInt(11, po->cc().IsPersistent());
>>>>>>add_smt.BindInt(12, po->cc().IsPersistent());
>>>>>>add_smt.BindInt( 13, CookiePriorityToDBCookiePriority(po->cc().Priority()));
>>>>>>if (!add_smt.Run()) {
>>>>>>>>DLOG(WARNING) << "Could not add a cookie to the DB.";
>>>>>>>> RecordCookieCommitProblem(COOKIE_COMMIT_PROBLEM_ADD);
>>>>>>>>trouble = true;
>>>>>>}
>>>> break;
可以看到 crypto_->EncryptString(po->cc().Value(), &encrypted_value)
将cookie值加密，后面赋值给 add_smt.BindBlob(4, encrypted_value.data(),
sql插入的第4个字段，再往上看，可以看到sql过程创建的方法如下：
sql::Statement add_smt(db()->GetCachedStatement(
SQL_FROM_HERE,
// TODO(chlily): These are out of order with respect to the schema
// declaration. Fix this.
"INSERT INTO cookies (creation_utc, host_key, name, value, "
"encrypted_value, path, expires_utc, is_secure, is_httponly, "
"samesite, last_access_utc, has_expires, is_persistent, priority) "
"VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?)"));
可以看到第4个字段为表单的encrypted_value字段，至此分析完成。