dpapi-core 0.1.0

use forensicnomicon::dpapi::{CHROME_COOKIE_V10, CHROME_COOKIE_V20};

use crate::error::DpapiError;

/// How a Chrome/Chromium cookie value is encoded in heap memory.
#[derive(Debug, PartialEq)]
pub enum ChromeCookieEncoding {
    /// Plaintext — no encryption prefix detected.
    Raw,
    /// Classic DPAPI blob (prefix `DPAPI`, 5 bytes). Windows 7 / no App-Bound.
    DpapiBlob(Vec<u8>),
    /// AES-256-GCM v10: `v10` + 12-byte nonce + ciphertext + 16-byte tag.
    V10 {
        nonce: [u8; 12],
        ciphertext: Vec<u8>,
    },
    /// AES-256-GCM v20 (Chrome 127+): same wire format as v10.
    V20 {
        nonce: [u8; 12],
        ciphertext: Vec<u8>,
    },
}

/// Detect the encoding of a raw `encrypted_value` blob from Chrome's Cookies DB.
pub fn detect_chrome_cookie_encoding(data: &[u8]) -> ChromeCookieEncoding {
    // v10/v20 require at least 3 (prefix) + 12 (nonce) = 15 bytes
    if data.len() > 15 {
        if data.starts_with(CHROME_COOKIE_V20) {
            let mut nonce = [0u8; 12];
            nonce.copy_from_slice(&data[3..15]);
            return ChromeCookieEncoding::V20 {
                nonce,
                ciphertext: data[15..].to_vec(),
            };
        }
        if data.starts_with(CHROME_COOKIE_V10) {
            let mut nonce = [0u8; 12];
            nonce.copy_from_slice(&data[3..15]);
            return ChromeCookieEncoding::V10 {
                nonce,
                ciphertext: data[15..].to_vec(),
            };
        }
    }
    if data.starts_with(b"DPAPI") {
        return ChromeCookieEncoding::DpapiBlob(data[5..].to_vec());
    }
    ChromeCookieEncoding::Raw
}

/// Decrypt a v10/v20 AES-256-GCM cookie value.
/// `key` is the 32-byte AES key from Chrome's `Local State` (already decrypted).
pub fn decrypt_v10_cookie(
    nonce: &[u8; 12],
    ciphertext: &[u8],
    key: &[u8; 32],
) -> Result<Vec<u8>, DpapiError> {
    #[allow(deprecated)]
    // from_slice deprecated in generic-array 1.x; aes-gcm 0.10 still uses 0.14
    use aes_gcm::{
        aead::{Aead, Nonce},
        Aes256Gcm, KeyInit,
    };
    let cipher = Aes256Gcm::new_from_slice(key).map_err(|_| DpapiError::InvalidKeyLength)?;
    #[allow(deprecated)]
    let nonce_ga = Nonce::<Aes256Gcm>::from_slice(nonce);
    cipher
        .decrypt(nonce_ga, ciphertext)
        .map_err(|_| DpapiError::DecryptionFailed)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn detect_v10_prefix() {
        let mut data = vec![0u8; 20];
        data[0..3].copy_from_slice(b"v10");
        let enc = detect_chrome_cookie_encoding(&data);
        assert!(matches!(enc, ChromeCookieEncoding::V10 { .. }));
    }

    #[test]
    fn detect_v20_prefix() {
        let mut data = vec![0u8; 20];
        data[0..3].copy_from_slice(b"v20");
        let enc = detect_chrome_cookie_encoding(&data);
        assert!(matches!(enc, ChromeCookieEncoding::V20 { .. }));
    }

    #[test]
    fn detect_dpapi_prefix() {
        let data = b"DPAPI\x00\x01\x02\x03".to_vec();
        let enc = detect_chrome_cookie_encoding(&data);
        assert!(matches!(enc, ChromeCookieEncoding::DpapiBlob(_)));
    }

    #[test]
    fn detect_plaintext_is_raw() {
        let enc = detect_chrome_cookie_encoding(b"plaintext_value");
        assert_eq!(enc, ChromeCookieEncoding::Raw);
    }

    #[test]
    #[allow(deprecated)]
    fn decrypt_v10_roundtrip() {
        use aes_gcm::{
            aead::{Aead, Nonce},
            Aes256Gcm, KeyInit,
        };
        let key = [0x42u8; 32];
        let nonce_bytes = [0x11u8; 12];
        let plaintext = b"session_token_value";
        let cipher = Aes256Gcm::new_from_slice(&key).unwrap();
        #[allow(deprecated)]
        let nonce = Nonce::<Aes256Gcm>::from_slice(&nonce_bytes);
        let ciphertext = cipher.encrypt(nonce, plaintext.as_ref()).unwrap();
        let recovered = decrypt_v10_cookie(&nonce_bytes, &ciphertext, &key).expect("ok");
        assert_eq!(recovered, plaintext);
    }
}