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Return errors from decode_payload #45

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05fc94d
Return errors from decode_payload
KiKoS0 May 24, 2022
d783285
Include test case for the payload decoding fix
KiKoS0 Jun 14, 2022
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16 changes: 10 additions & 6 deletions lib/ex_crypto.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -461,12 +461,16 @@ defmodule ExCrypto do
"""
@spec decode_payload(binary) :: {:ok, {binary, binary, binary}} | {:error, binary}
def decode_payload(encoded_parts) do
{:ok, decoded_parts} = Base.url_decode64(encoded_parts)
decoded_length = byte_size(decoded_parts)
iv = Kernel.binary_part(decoded_parts, 0, 16)
cipher_text = Kernel.binary_part(decoded_parts, 16, decoded_length - 32)
cipher_tag = Kernel.binary_part(decoded_parts, decoded_length, -16)
{:ok, {iv, cipher_text, cipher_tag}}
with {:ok, decoded_parts} <- Base.url_decode64(encoded_parts),
decoded_length when decoded_length >= 32 <- byte_size(decoded_parts) do
iv = Kernel.binary_part(decoded_parts, 0, 16)
cipher_text = Kernel.binary_part(decoded_parts, 16, decoded_length - 32)
cipher_tag = Kernel.binary_part(decoded_parts, decoded_length, -16)
{:ok, {iv, cipher_text, cipher_tag}}
else
:error -> {:error, "invalid base64 payload"}
_ -> {:error, "invalid decoded payload length"}
end
end

@doc false
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18 changes: 14 additions & 4 deletions test/ex_crypto_test.exs
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Expand Up @@ -140,6 +140,13 @@ defmodule ExCryptoTest do
assert(cipher_tag == pc_tag)
end

test "errors decoding invalid payloads" do
assert {:error, "invalid base64 payload"} = ExCrypto.decode_payload(".")

assert {:error, "invalid decoded payload length"} =
Base.url_encode64("AAAAAAAAAAAAAAAA") |> ExCrypto.decode_payload()
end

test "test aes_cbc encrypt with auto-IV (256 bit key)" do
{:ok, aes_256_key} = ExCrypto.generate_aes_key(:aes_256, :bytes)

Expand Down Expand Up @@ -185,7 +192,8 @@ defmodule ExCryptoTest do
{:ok, {_ad, payload}} = ExCrypto.encrypt(aes_256_key, a_data, iv, clear_text)
{_c_iv, cipher_text, cipher_tag} = payload
# decrypt
assert {:error, :decrypt_failed} = ExCrypto.decrypt(aes_256_key, "wrong ad", iv, cipher_text, cipher_tag)
assert {:error, :decrypt_failed} =
ExCrypto.decrypt(aes_256_key, "wrong ad", iv, cipher_text, cipher_tag)
end

test "errors decrypting with argument error (cipher_text)" do
Expand All @@ -203,9 +211,11 @@ defmodule ExCryptoTest do
txt_joined = IO.iodata_to_binary(txt)
aad = "Some bytes"

cipher_text = <<240, 130, 38, 96, 130, 241, 189, 52, 3, 190, 179, 213, 132, 1, 72, 192, 103,
176, 90, 104, 15, 71, 158>>
cipher_tag = <<131, 47, 45, 91, 142, 85, 9, 244, 21, 141, 214, 71, 31, 135, 2, 155>>
cipher_text =
<<240, 130, 38, 96, 130, 241, 189, 52, 3, 190, 179, 213, 132, 1, 72, 192, 103, 176, 90, 104,
15, 71, 158>>

cipher_tag = <<131, 47, 45, 91, 142, 85, 9, 244, 21, 141, 214, 71, 31, 135, 2, 155>>

# encrypt
{:ok, {^aad, {^iv, ^cipher_text, ^cipher_tag}}} = ExCrypto.encrypt(key, aad, iv, txt)
Expand Down