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std/sysrand for Windows XP #19538

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std/sysrand for Windows XP #19538

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122 changes: 102 additions & 20 deletions lib/std/sysrand.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -16,19 +16,20 @@
## and should be unpredictable enough for cryptographic applications,
## though its exact quality depends on the OS implementation.
##
## | Targets | Implementation |
## | :--- | ----: |
## | Windows | `BCryptGenRandom`_ |
## | Linux | `getrandom`_ |
## | MacOSX | `getentropy`_ |
## | iOS | `SecRandomCopyBytes`_ |
## | OpenBSD | `getentropy openbsd`_ |
## | FreeBSD | `getrandom freebsd`_ |
## | JS (Web Browser) | `getRandomValues`_ |
## | Node.js | `randomFillSync`_ |
## | Other Unix platforms | `/dev/urandom`_ |
## | Targets | Implementation |
## | :--- | ----: |
## | Windows | `BCryptGenRandom`_ or `CryptGenRandom`_ |
## | Linux | `getrandom`_ |
## | MacOSX | `getentropy`_ |
## | iOS | `SecRandomCopyBytes`_ |
## | OpenBSD | `getentropy openbsd`_ |
## | FreeBSD | `getrandom freebsd`_ |
## | JS (Web Browser) | `getRandomValues`_ |
## | Node.js | `randomFillSync`_ |
## | Other Unix platforms | `/dev/urandom`_ |
##
## .. _BCryptGenRandom: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
## .. _CryptGenRandom: https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-cryptgenrandom
## .. _getrandom: https://man7.org/linux/man-pages/man2/getrandom.2.html
## .. _getentropy: https://www.unix.com/man-page/mojave/2/getentropy
## .. _SecRandomCopyBytes: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
Expand Down Expand Up @@ -134,35 +135,116 @@ when defined(js):
assign(dest, leftArray, result, left)

elif defined(windows):
import std/[dynlib, exitprocs]

type
PVOID = pointer
BCRYPT_ALG_HANDLE = PVOID
PUCHAR = ptr uint8
NTSTATUS = clong
ULONG = culong
HCRYPTPROV = pointer
LPCSTR = cstring
DWORD = cuint
BOOL = cint
BYTE = byte

BCryptGenRandom = proc(hAlgorithm: BCRYPT_ALG_HANDLE, pbBuffer: PUCHAR, cbBuffer,
dwFlags: ULONG): NTSTATUS {.stdcall, gcsafe.}
CryptGenRandom = proc(hProv: HCRYPTPROV, dwLen: DWORD, pbBuffer: ptr BYTE): BOOL {.stdcall,
gcsafe.}
CryptAcquireContextA = proc(phProv: HCRYPTPROV, szContainer, szProvider: LPCSTR, dwProvType,
dwFlags: DWORD): BOOL {.stdcall.}
CryptReleaseContext = proc(hProv: HCRYPTPROV, dwFlags: DWORD): BOOL {.stdcall.}

WinCRngType = enum
WinCRngNone, WinCRngBCrypt, WinCRngWinCrypt

WinCRng = object
libHandle: LibHandle
case cRngType: WinCRngType
of WinCRngBCrypt:
bCryptGenRandom: BCryptGenRandom
of WinCRngWinCrypt:
cryptGenRandom: CryptGenRandom
hProv: HCRYPTPROV
of WinCRngNone:
discard

const
PROV_RSA_FULL = DWORD(0x00000001)
CRYPT_VERIFYCONTEXT = DWORD(0xF0000000)
STATUS_SUCCESS = 0x00000000
BCRYPT_USE_SYSTEM_PREFERRED_RNG = 0x00000002

proc bCryptGenRandom(
hAlgorithm: BCRYPT_ALG_HANDLE,
pbBuffer: PUCHAR,
cbBuffer: ULONG,
dwFlags: ULONG
): NTSTATUS {.stdcall, importc: "BCryptGenRandom", dynlib: "Bcrypt.dll".}

var winCRng = WinCRng(libHandle: nil, cRngType: WinCRngNone)

proc closeWinCRng() =
if winCRng.cRngType == WinCRngWinCrypt:
let getProcAddr = symAddr(winCRng.libHandle, "CryptReleaseContext")
if not isNil(getProcAddr):
let call = cast[CryptReleaseContext](getProcAddr)
discard call(winCRng.hProv, DWORD(0))
if not isNil(winCRng.libHandle):
unloadLib(winCRng.libHandle)

proc loadBCrypt() =
var bcrypt = WinCRng(libHandle: nil, cRngType: WinCRngBCrypt, bCryptGenRandom: nil)
bcrypt.libHandle = loadLib("Bcrypt.dll")
if not isNil(bcrypt.libHandle):
let procAddr = symAddr(bcrypt.libHandle, "BCryptGenRandom")
if not isNil(procAddr):
var buf: uint
bcrypt.bCryptGenRandom = cast[BCryptGenRandom](procAddr)
if bcrypt.bCryptGenRandom(nil, cast[PUCHAR](addr buf), ULONG(sizeof(buf)),
BCRYPT_USE_SYSTEM_PREFERRED_RNG) == STATUS_SUCCESS:
winCRng = bcrypt
if winCRng.cRngType == WinCRngNone and not isNil(bcrypt.libHandle):
unloadLib(bcrypt.libHandle)

proc loadWinCrypt() =
var crypt = WinCRng(libHandle: nil, cRngType: WinCRngWinCrypt, cryptGenRandom: nil, hProv: nil)
crypt.libHandle = loadLib("Advapi32.dll")
if not isNil(crypt.libHandle):
let procAddr = symAddr(crypt.libHandle, "CryptGenRandom")
if not isNil(procAddr):
let getProcAddr = symAddr(crypt.libHandle, "CryptAcquireContextA")
if not isNil(getProcAddr):
let cryptAcquireContext = cast[CryptAcquireContextA](getProcAddr)
if cryptAcquireContext(addr crypt.hProv, nil, nil, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT) != 0:
var buf: uint
crypt.cryptGenRandom = cast[CryptGenRandom](procAddr)
if crypt.cryptGenRandom(crypt.hProv, sizeof(buf).DWORD, cast[ptr BYTE](addr buf)) != 0:
winCRng = crypt
if winCRng.cRngType == WinCRngNone and not isNil(crypt.libHandle):
unloadLib(crypt.libHandle)

proc initWinCRng() =
loadBCrypt()
if winCRng.cRngType == WinCRngNone:
loadWinCrypt()
addExitProc(closeWinCRng)

proc randomBytes(pbBuffer: pointer, cbBuffer: Natural): int {.inline.} =
bCryptGenRandom(nil, cast[PUCHAR](pbBuffer), ULONG(cbBuffer),
BCRYPT_USE_SYSTEM_PREFERRED_RNG)
case winCRng.cRngType
of WinCRngBCrypt:
if winCRng.bCryptGenRandom(nil, cast[PUCHAR](pbBuffer), ULONG(cbBuffer),
BCRYPT_USE_SYSTEM_PREFERRED_RNG) != STATUS_SUCCESS:
result = 1
of WinCRngWinCrypt:
if winCRng.cryptGenRandom(winCRng.hProv, DWORD(cbBuffer), cast[ptr BYTE](pbBuffer)) == 0:
result = 1
of WinCRngNone:
result = 1

template urandomImpl(result: var int, dest: var openArray[byte]) =
let size = dest.len
if size == 0:
return

result = randomBytes(addr dest[0], size)

initWinCRng()

elif defined(linux) and not defined(nimNoGetRandom) and not defined(emscripten):
# TODO using let, pending bootstrap >= 1.4.0
Expand Down