wechat_profile/
dat.rs

1use crate::{ImageDatKey, ProfileError, Result};
2use aes::Aes128;
3use cipher::{generic_array::GenericArray, BlockDecrypt, BlockEncrypt, KeyInit};
4use serde::{Deserialize, Serialize};
5use zeroize::Zeroizing;
6
7const MAGIC: &[u8; 6] = b"\x07\x08V2\x08\x07";
8pub const MAX_DAT_PLAINTEXT_BYTES: usize = 64 * 1024 * 1024;
9#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
10#[serde(rename_all = "camelCase", deny_unknown_fields)]
11pub struct DatLayout {
12    pub aes_plain_bytes: u32,
13    pub xor_bytes: u32,
14    pub control_byte: u8,
15}
16impl DatLayout {
17    pub fn observed(plain_len: usize) -> Result<Self> {
18        if !(1024..=MAX_DAT_PLAINTEXT_BYTES).contains(&plain_len) {
19            return Err(ProfileError::InvalidDat);
20        }
21        Ok(Self {
22            aes_plain_bytes: 1024,
23            xor_bytes: (plain_len - 1024).min(1024 * 1024) as u32,
24            control_byte: 1,
25        })
26    }
27    fn cipher_bytes(self) -> Result<usize> {
28        if self.aes_plain_bytes == 0
29            || self.aes_plain_bytes as usize > MAX_DAT_PLAINTEXT_BYTES
30            || self.xor_bytes as usize > MAX_DAT_PLAINTEXT_BYTES
31            || self.control_byte != 1
32        {
33            return Err(ProfileError::InvalidDat);
34        }
35        Ok((self.aes_plain_bytes as usize / 16 + 1) * 16)
36    }
37}
38pub fn parse_dat_v2(data: &[u8]) -> Result<DatLayout> {
39    if data.len() < 15
40        || data.len() > MAX_DAT_PLAINTEXT_BYTES + 31
41        || data.get(..6) != Some(MAGIC.as_slice())
42    {
43        return Err(ProfileError::InvalidDat);
44    }
45    let mut h = [0u8; 4];
46    h.copy_from_slice(&data[6..10]);
47    let mut t = [0u8; 4];
48    t.copy_from_slice(&data[10..14]);
49    let layout = DatLayout {
50        aes_plain_bytes: u32::from_le_bytes(h),
51        xor_bytes: u32::from_le_bytes(t),
52        control_byte: data[14],
53    };
54    let cipher = layout.cipher_bytes()?;
55    if data.len() < 15 + cipher + layout.xor_bytes as usize {
56        return Err(ProfileError::InvalidDat);
57    }
58    Ok(layout)
59}
60/// Independent V2 framing decode. ECB/XOR is not authenticated encryption;
61/// callers must separately validate image format/dimensions before rendering.
62pub fn decode_dat_v2(data: &[u8], key: &ImageDatKey) -> Result<(Vec<u8>, DatLayout)> {
63    let layout = parse_dat_v2(data)?;
64    let end = 15 + layout.cipher_bytes()?;
65    let cipher = Aes128::new_from_slice(key.aes.expose()).map_err(|_| ProfileError::InvalidDat)?;
66    let mut head = Zeroizing::new(data[15..end].to_vec());
67    for b in head.chunks_exact_mut(16) {
68        cipher.decrypt_block(GenericArray::from_mut_slice(b));
69    }
70    let pad = usize::from(*head.last().ok_or(ProfileError::InvalidDat)?);
71    if !(1..=16).contains(&pad)
72        || pad > head.len()
73        || head[head.len() - pad..]
74            .iter()
75            .any(|b| usize::from(*b) != pad)
76    {
77        return Err(ProfileError::InvalidDat);
78    }
79    let unpadded = head.len() - pad;
80    head.truncate(unpadded);
81    if head.len() != layout.aes_plain_bytes as usize {
82        return Err(ProfileError::InvalidDat);
83    }
84    let tail = data.len() - layout.xor_bytes as usize;
85    let output_len = head.len() + tail - end + layout.xor_bytes as usize;
86    if output_len > MAX_DAT_PLAINTEXT_BYTES {
87        return Err(ProfileError::ResourceLimit);
88    }
89    let mut output = Vec::with_capacity(output_len);
90    output.extend_from_slice(&head);
91    output.extend_from_slice(&data[end..tail]);
92    output.extend(data[tail..].iter().map(|b| b ^ key.xor));
93    Ok((output, layout))
94}
95pub fn encode_dat_v2(
96    plaintext: &[u8],
97    key: &ImageDatKey,
98    layout: Option<DatLayout>,
99) -> Result<Vec<u8>> {
100    if plaintext.len() > MAX_DAT_PLAINTEXT_BYTES {
101        return Err(ProfileError::ResourceLimit);
102    }
103    let layout = match layout {
104        Some(l) => l,
105        None => DatLayout::observed(plaintext.len())?,
106    };
107    let cipher_bytes = layout.cipher_bytes()?;
108    let h = layout.aes_plain_bytes as usize;
109    let t = layout.xor_bytes as usize;
110    if h.checked_add(t).is_none_or(|v| v > plaintext.len()) {
111        return Err(ProfileError::InvalidDat);
112    }
113    let cipher = Aes128::new_from_slice(key.aes.expose()).map_err(|_| ProfileError::InvalidDat)?;
114    let mut head = Zeroizing::new(plaintext[..h].to_vec());
115    head.resize(cipher_bytes, (cipher_bytes - h) as u8);
116    for b in head.chunks_exact_mut(16) {
117        cipher.encrypt_block(GenericArray::from_mut_slice(b));
118    }
119    let mut output = Vec::with_capacity(15 + cipher_bytes + plaintext.len() - h);
120    output.extend_from_slice(MAGIC);
121    output.extend_from_slice(&layout.aes_plain_bytes.to_le_bytes());
122    output.extend_from_slice(&layout.xor_bytes.to_le_bytes());
123    output.push(layout.control_byte);
124    output.extend_from_slice(&head);
125    output.extend_from_slice(&plaintext[h..plaintext.len() - t]);
126    output.extend(plaintext[plaintext.len() - t..].iter().map(|b| b ^ key.xor));
127    Ok(output)
128}
wechat_profile/dat.rs

wechat_profile/
dat.rs
