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prp: refactor #47

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49 changes: 21 additions & 28 deletions nimutils/prp.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -47,52 +47,45 @@ type PrpCtx = object
round1, round2, round3, round4: string

proc initPrpContext(key, nonce, msg: string): PrpCtx =
var ks: string

result.contents = msg

if key.len() notin [16, 24, 32]:
raise newException(ValueError, "Invalid AES key size")

if nonce.len() != 16:
raise newException(ValueError, "Nonce must be 16 bytes.")

ks = aesPrfOneShot(key, 16*4, nonce)

result.round1 = ks[0 ..< 16]
result.round2 = ks[16 ..< 32]
result.round3 = ks[32 ..< 48]
result.round4 = ks[48 ..< 64]
let ks = aesPrfOneShot(key, 16*4, nonce)

{.emit: """
void xor_in_place(char *out, char *s2, int len) {
for (int i = 0; i < len; i++) {
out[i] ^= s2[i];
}
}
"""}
result = PrpCtx(
contents: msg,
round1: ks[0 ..< 16],
round2: ks[16 ..< 32],
round3: ks[32 ..< 48],
round4: ks[48 ..< 64],
)

proc xor_in_place(o: pointer, s: cstring, i: cint):
void {.cdecl, importc, nodecl.}
proc xorInPlace(a: var string, b: string, n: int) =
assert a.len >= n
assert b.len >= n
for i in 0 ..< n:
a[i] = char(a[i].uint8 xor b[i].uint8)

proc runHmacPrf(ctx: PrpCtx, key: string) =
var toXor = key.hmacSha3(ctx.contents[16..^1])

xor_in_place(addr ctx.contents[0], cstring(toXor), cint(16))
proc runHmacPrf(ctx: var PrpCtx, key: string) =
let toXor = key.hmacSha3(ctx.contents[16..^1])
xorInPlace(ctx.contents, toXor, 16)

proc runCtrPrf(ctx: PrpCtx, key: string) =
aesCtrInPlaceOneShot(key, addr ctx.contents[16], cint(len(ctx.contents) - 16))

template round1(ctx: PrpCtx) =
proc round1(ctx: var PrpCtx) =
ctx.runHmacPrf(ctx.round1)

template round2(ctx: PrpCtx) =
proc round2(ctx: var PrpCtx) =
ctx.runCtrPrf(ctx.round2)

template round3(ctx: PrpCtx) =
proc round3(ctx: var PrpCtx) =
ctx.runHmacPrf(ctx.round3)

template round4(ctx: PrpCtx) =
proc round4(ctx: var PrpCtx) =
ctx.runCtrPrf(ctx.round4)

proc prp*(key, toEncrypt: string, nonce: var string, randomNonce = true):
Expand Down Expand Up @@ -132,7 +125,7 @@ proc prp*(key, toEncrypt: string, nonce: var string, randomNonce = true):
ctx.round3()
ctx.round4()

return $(ctx.contents)
return ctx.contents

proc brb*(key, toDecrypt: string, nonce: string): string =
## The reverse permutation for our 4-round Luby Rackoff PRP.
Expand Down