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Add more descriptive error message to HDKF max length #17

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merged 1 commit into from
Mar 31, 2024
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Add more descriptive error message to HDKF max length #17

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12 changes: 8 additions & 4 deletions protocol/src/hkdf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,11 +11,13 @@ const MAX_OUTPUT_BLOCKS: usize = 255;

/// Size of output exceeds maximum length allowed.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct MaxLengthError;
pub struct MaxLengthError {
max: usize,
}

impl fmt::Display for MaxLengthError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "too large output")
write!(f, "exceeds {} byte max output material limit", self.max)
}
}

Expand All @@ -40,9 +42,11 @@ impl<T: Hash> Hkdf<T> {

/// Expand the key to generate output key material in okm.
pub fn expand(&self, info: &[u8], okm: &mut [u8]) -> Result<(), MaxLengthError> {
// Length of output keying material must be less than 255 * hash length.
// Length of output keying material in bytes must be less than 255 * hash length.
if okm.len() > (MAX_OUTPUT_BLOCKS * T::LEN) {
return Err(MaxLengthError);
return Err(MaxLengthError {
max: MAX_OUTPUT_BLOCKS * T::LEN,
});
}

// Counter starts at "1" based on RFC5869 spec and is committed to in the hash.
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