windows: add support for DPAPI

DPAPI allows machine or user-based blob encryption, using APIs from
crypt32:

https://docs.microsoft.com/en-us/windows/win32/api/dpapi/nf-dpapi-cryptunprotectdata
https://docs.microsoft.com/en-us/windows/win32/api/dpapi/nf-dpapi-cryptprotectdata

Change-Id: I57fb4f1877a5fb7629809e79111cbfa02b11cca3
Reviewed-on: https://go-review.googlesource.com/c/sys/+/285716
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

windows/syscall_windows.go

@@ -285,6 +285,8 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	CertFindExtension(objId *byte, countExtensions uint32, extensions *CertExtension) (ret *CertExtension) = crypt32.CertFindExtension
 //sys	CryptQueryObject(objectType uint32, object unsafe.Pointer, expectedContentTypeFlags uint32, expectedFormatTypeFlags uint32, flags uint32, msgAndCertEncodingType *uint32, contentType *uint32, formatType *uint32, certStore *Handle, msg *Handle, context *unsafe.Pointer) (err error) = crypt32.CryptQueryObject
 //sys	CryptDecodeObject(encodingType uint32, structType *byte, encodedBytes *byte, lenEncodedBytes uint32, flags uint32, decoded unsafe.Pointer, decodedLen *uint32) (err error) = crypt32.CryptDecodeObject
+//sys	CryptProtectData(dataIn *DataBlob, name *uint16, optionalEntropy *DataBlob, reserved uintptr, promptStruct *CryptProtectPromptStruct, flags uint32, dataOut *DataBlob) (err error) = crypt32.CryptProtectData
+//sys	CryptUnprotectData(dataIn *DataBlob, name **uint16, optionalEntropy *DataBlob, reserved uintptr, promptStruct *CryptProtectPromptStruct, flags uint32, dataOut *DataBlob) (err error) = crypt32.CryptUnprotectData
 //sys	WinVerifyTrustEx(hwnd HWND, actionId *GUID, data *WinTrustData) (ret error) = wintrust.WinVerifyTrustEx
 //sys	RegOpenKeyEx(key Handle, subkey *uint16, options uint32, desiredAccess uint32, result *Handle) (regerrno error) = advapi32.RegOpenKeyExW
 //sys	RegCloseKey(key Handle) (regerrno error) = advapi32.RegCloseKey

windows/types_windows.go

@@ -498,6 +498,22 @@ const (
 	SECURITY_FLAG_IGNORE_WRONG_USAGE       = 0x00000200
 	SECURITY_FLAG_IGNORE_CERT_CN_INVALID   = 0x00001000
 	SECURITY_FLAG_IGNORE_CERT_DATE_INVALID = 0x00002000
+
+	/* Flags for Crypt[Un]ProtectData */
+	CRYPTPROTECT_UI_FORBIDDEN      = 0x1
+	CRYPTPROTECT_LOCAL_MACHINE     = 0x4
+	CRYPTPROTECT_CRED_SYNC         = 0x8
+	CRYPTPROTECT_AUDIT             = 0x10
+	CRYPTPROTECT_NO_RECOVERY       = 0x20
+	CRYPTPROTECT_VERIFY_PROTECTION = 0x40
+	CRYPTPROTECT_CRED_REGENERATE   = 0x80
+
+	/* Flags for CryptProtectPromptStruct */
+	CRYPTPROTECT_PROMPT_ON_UNPROTECT   = 1
+	CRYPTPROTECT_PROMPT_ON_PROTECT     = 2
+	CRYPTPROTECT_PROMPT_RESERVED       = 4
+	CRYPTPROTECT_PROMPT_STRONG         = 8
+	CRYPTPROTECT_PROMPT_REQUIRE_STRONG = 16
 )
 
 const (
@@ -1337,6 +1353,13 @@ type CertStrongSignPara struct {
 	InfoOrSerializedInfoOrOID unsafe.Pointer
 }
 
+type CryptProtectPromptStruct struct {
+	Size        uint32
+	PromptFlags uint32
+	App         HWND
+	Prompt      *uint16
+}
+
 type WinTrustData struct {
 	Size                            uint32
 	PolicyCallbackData              uintptr

windows/zsyscall_windows.go

@@ -155,7 +155,9 @@ var (
 	procCertOpenSystemStoreW                                 = modcrypt32.NewProc("CertOpenSystemStoreW")
 	procCertVerifyCertificateChainPolicy                     = modcrypt32.NewProc("CertVerifyCertificateChainPolicy")
 	procCryptDecodeObject                                    = modcrypt32.NewProc("CryptDecodeObject")
+	procCryptProtectData                                     = modcrypt32.NewProc("CryptProtectData")
 	procCryptQueryObject                                     = modcrypt32.NewProc("CryptQueryObject")
+	procCryptUnprotectData                                   = modcrypt32.NewProc("CryptUnprotectData")
 	procPFXImportCertStore                                   = modcrypt32.NewProc("PFXImportCertStore")
 	procDnsNameCompare_W                                     = moddnsapi.NewProc("DnsNameCompare_W")
 	procDnsQuery_W                                           = moddnsapi.NewProc("DnsQuery_W")
@@ -1275,6 +1277,14 @@ func CryptDecodeObject(encodingType uint32, structType *byte, encodedBytes *byte
 	return
 }
 
+func CryptProtectData(dataIn *DataBlob, name *uint16, optionalEntropy *DataBlob, reserved uintptr, promptStruct *CryptProtectPromptStruct, flags uint32, dataOut *DataBlob) (err error) {
+	r1, _, e1 := syscall.Syscall9(procCryptProtectData.Addr(), 7, uintptr(unsafe.Pointer(dataIn)), uintptr(unsafe.Pointer(name)), uintptr(unsafe.Pointer(optionalEntropy)), uintptr(reserved), uintptr(unsafe.Pointer(promptStruct)), uintptr(flags), uintptr(unsafe.Pointer(dataOut)), 0, 0)
+	if r1 == 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
 func CryptQueryObject(objectType uint32, object unsafe.Pointer, expectedContentTypeFlags uint32, expectedFormatTypeFlags uint32, flags uint32, msgAndCertEncodingType *uint32, contentType *uint32, formatType *uint32, certStore *Handle, msg *Handle, context *unsafe.Pointer) (err error) {
 	r1, _, e1 := syscall.Syscall12(procCryptQueryObject.Addr(), 11, uintptr(objectType), uintptr(object), uintptr(expectedContentTypeFlags), uintptr(expectedFormatTypeFlags), uintptr(flags), uintptr(unsafe.Pointer(msgAndCertEncodingType)), uintptr(unsafe.Pointer(contentType)), uintptr(unsafe.Pointer(formatType)), uintptr(unsafe.Pointer(certStore)), uintptr(unsafe.Pointer(msg)), uintptr(unsafe.Pointer(context)), 0)
 	if r1 == 0 {
@@ -1283,6 +1293,14 @@ func CryptQueryObject(objectType uint32, object unsafe.Pointer, expectedContentT
 	return
 }
 
+func CryptUnprotectData(dataIn *DataBlob, name **uint16, optionalEntropy *DataBlob, reserved uintptr, promptStruct *CryptProtectPromptStruct, flags uint32, dataOut *DataBlob) (err error) {
+	r1, _, e1 := syscall.Syscall9(procCryptUnprotectData.Addr(), 7, uintptr(unsafe.Pointer(dataIn)), uintptr(unsafe.Pointer(name)), uintptr(unsafe.Pointer(optionalEntropy)), uintptr(reserved), uintptr(unsafe.Pointer(promptStruct)), uintptr(flags), uintptr(unsafe.Pointer(dataOut)), 0, 0)
+	if r1 == 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
 func PFXImportCertStore(pfx *CryptDataBlob, password *uint16, flags uint32) (store Handle, err error) {
 	r0, _, e1 := syscall.Syscall(procPFXImportCertStore.Addr(), 3, uintptr(unsafe.Pointer(pfx)), uintptr(unsafe.Pointer(password)), uintptr(flags))
 	store = Handle(r0)