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use crate::prelude::*;
use block_modes::BlockMode as _;
use hmac::Mac as _;
pub struct CipherString {
ty: u8,
iv: Vec<u8>,
ciphertext: Vec<u8>,
mac: Option<Vec<u8>>,
}
impl CipherString {
pub fn new(s: &str) -> Result<Self> {
let parts: Vec<&str> = s.split('.').collect();
if parts.len() != 2 {
return Err(Error::InvalidCipherString);
}
let ty = parts[0].as_bytes();
if ty.len() != 1 {
return Err(Error::InvalidCipherString);
}
let ty = ty[0] - b'0';
let contents = parts[1];
let parts: Vec<&str> = contents.split('|').collect();
if parts.len() < 2 || parts.len() > 3 {
return Err(Error::InvalidCipherString);
}
let iv =
base64::decode(parts[0]).context(crate::error::InvalidBase64)?;
let ciphertext =
base64::decode(parts[1]).context(crate::error::InvalidBase64)?;
let mac = if parts.len() > 2 {
Some(
base64::decode(parts[2])
.context(crate::error::InvalidBase64)?,
)
} else {
None
};
Ok(Self {
ty,
iv,
ciphertext,
mac,
})
}
pub fn decrypt(&self, enc_key: &[u8], mac_key: &[u8]) -> Result<Vec<u8>> {
if self.ty != 2 {
unimplemented!()
}
if let Some(mac) = &self.mac {
let mut digest = hmac::Hmac::<sha2::Sha256>::new_varkey(mac_key)
.map_err(|_| Error::InvalidMacKey)?;
digest.input(&self.iv);
digest.input(&self.ciphertext);
let calculated_mac = digest.result().code();
if !macs_equal(mac, &calculated_mac, mac_key)? {
return Err(Error::InvalidMac);
}
}
let cipher = block_modes::Cbc::<
aes::Aes256,
block_modes::block_padding::Pkcs7,
>::new_var(enc_key, &self.iv)
.context(crate::error::CreateBlockMode)?;
cipher
.decrypt_vec(&self.ciphertext)
.context(crate::error::Decrypt)
}
}
fn macs_equal(mac1: &[u8], mac2: &[u8], mac_key: &[u8]) -> Result<bool> {
let mut digest = hmac::Hmac::<sha2::Sha256>::new_varkey(mac_key)
.map_err(|_| Error::InvalidMacKey)?;
digest.input(mac1);
let hmac1 = digest.result().code();
let mut digest = hmac::Hmac::<sha2::Sha256>::new_varkey(mac_key)
.map_err(|_| Error::InvalidMacKey)?;
digest.input(mac2);
let hmac2 = digest.result().code();
Ok(hmac1 == hmac2)
}
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