Skip to content

Bound PKCS#1 modulus sizes before bigint conversion #793

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
tarcieri merged 1 commit into from
Nov 9, 2026
Merged

Bound PKCS#1 modulus sizes before bigint conversion #793

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
81 changes: 45 additions & 36 deletions src/encoding.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,7 +1,4 @@
//! PKCS#1 and PKCS#8 encoding support.
//!
//! Note: PKCS#1 support is achieved through a blanket impl of the
//! `pkcs1` crate's traits for types which impl the `pkcs8` crate's traits.

#![cfg(feature = "encoding")]

Expand All @@ -13,15 +10,41 @@ use core::convert::{TryFrom, TryInto};
use crypto_bigint::{BoxedUint, NonZero, Resize};
use pkcs8::{
Document, EncodePrivateKey, EncodePublicKey, ObjectIdentifier, SecretDocument,
der::{Decode, asn1::AsUintRef, asn1::OctetStringRef},
der::{
Decode,
asn1::{self, AsUintRef},
},
};
use zeroize::Zeroizing;

/// ObjectID for the RSA PSS keys
pub const ID_RSASSA_PSS: ObjectIdentifier = ObjectIdentifier::new_unwrap("1.2.840.113549.1.1.10");

/// Maximum allowed modulus size in bits.
#[allow(clippy::integer_division_remainder_used, reason = "constant")]
const MAX_MODULUS_BITS: usize = PublicKey::MAX_SIZE / 8;

// PKCS#1

/// Get the number of bits required to store a given `UintRef`.
fn bits_for_uint_ref(encoded_modulus: asn1::UintRef<'_>) -> pkcs1::Result<u32> {
u32::try_from(encoded_modulus.as_bytes().len())
.ok()
.and_then(|bytes| bytes.checked_mul(8))
.ok_or(pkcs1::Error::KeyMalformed)
}

/// Parse the modulus from an `asn1::UintRef`.
fn encoded_modulus_to_uint(encoded_modulus: asn1::UintRef<'_>) -> pkcs1::Result<BoxedUint> {
if encoded_modulus.as_bytes().len() > MAX_MODULUS_BITS {
return Err(pkcs1::Error::KeyMalformed);
}

let bits = bits_for_uint_ref(encoded_modulus)?;
uint_from_slice(encoded_modulus.as_bytes(), bits)
}

/// Convert the given byte slice into a [`BoxedUint`].
fn uint_from_slice(data: &[u8], bits: u32) -> pkcs1::Result<BoxedUint> {
BoxedUint::from_be_slice(data, bits).map_err(|_| pkcs1::Error::KeyMalformed)
}
Expand Down Expand Up @@ -49,14 +72,9 @@ impl<U: AsUintRef> TryFrom<pkcs1::RsaPrivateKey<U>> for PrivateKey {
return Err(pkcs1::Error::Version);
}

let bits = u32::try_from(pkcs1_key.modulus.as_uint_ref().as_bytes().len())
.map_err(|_| KeyMalformed)?
* 8;

let n = uint_from_slice(pkcs1_key.modulus.as_uint_ref().as_bytes(), bits)?;
let bits_e = u32::try_from(pkcs1_key.public_exponent.as_uint_ref().as_bytes().len())
.map_err(|_| KeyMalformed)?
* 8;
let n = encoded_modulus_to_uint(pkcs1_key.modulus.as_uint_ref())?;
let bits = n.bit_width();
let bits_e = bits_for_uint_ref(pkcs1_key.public_exponent.as_uint_ref())?;
let e = uint_from_slice(pkcs1_key.public_exponent.as_uint_ref().as_bytes(), bits_e)?;
let e = Option::from(e).ok_or(KeyMalformed)?;

Expand All @@ -75,14 +93,8 @@ impl<U: AsUintRef> TryFrom<pkcs1::RsaPublicKey<U>> for PublicKey {
fn try_from(pkcs1_key: pkcs1::RsaPublicKey<U>) -> pkcs1::Result<Self> {
use pkcs1::Error::KeyMalformed;

let bits = u32::try_from(pkcs1_key.modulus.as_uint_ref().as_bytes().len())
.map_err(|_| KeyMalformed)?
* 8;
let n = uint_from_slice(pkcs1_key.modulus.as_uint_ref().as_bytes(), bits)?;

let bits_e = u32::try_from(pkcs1_key.public_exponent.as_uint_ref().as_bytes().len())
.map_err(|_| KeyMalformed)?
* 8;
let n = encoded_modulus_to_uint(pkcs1_key.modulus.as_uint_ref())?;
let bits_e = bits_for_uint_ref(pkcs1_key.public_exponent.as_uint_ref())?;
let e = uint_from_slice(pkcs1_key.public_exponent.as_uint_ref().as_bytes(), bits_e)?;

PublicKey::new(n, e).map_err(|_| KeyMalformed)
Expand Down Expand Up @@ -126,14 +138,14 @@ impl pkcs1::EncodeRsaPrivateKey for PrivateKey {
);

Ok(SecretDocument::encode_msg(&pkcs1::RsaPrivateKey {
modulus: pkcs1::UintRef::new(&modulus)?,
public_exponent: pkcs1::UintRef::new(&public_exponent)?,
private_exponent: pkcs1::UintRef::new(&private_exponent)?,
prime1: pkcs1::UintRef::new(&prime1)?,
prime2: pkcs1::UintRef::new(&prime2)?,
exponent1: pkcs1::UintRef::new(&exponent1)?,
exponent2: pkcs1::UintRef::new(&exponent2)?,
coefficient: pkcs1::UintRef::new(&coefficient)?,
modulus: asn1::UintRef::new(&modulus)?,
public_exponent: asn1::UintRef::new(&public_exponent)?,
private_exponent: asn1::UintRef::new(&private_exponent)?,
prime1: asn1::UintRef::new(&prime1)?,
prime2: asn1::UintRef::new(&prime2)?,
exponent1: asn1::UintRef::new(&exponent1)?,
exponent2: asn1::UintRef::new(&exponent2)?,
coefficient: asn1::UintRef::new(&coefficient)?,
other_prime_infos: None,
})?)
}
Expand All @@ -145,8 +157,8 @@ impl pkcs1::EncodeRsaPublicKey for PublicKey {
let public_exponent = self.e().to_be_bytes();

Ok(Document::encode_msg(&pkcs1::RsaPublicKeyRef {
modulus: pkcs1::UintRef::new(&modulus)?,
public_exponent: pkcs1::UintRef::new(&public_exponent)?,
modulus: asn1::UintRef::new(&modulus)?,
public_exponent: asn1::UintRef::new(&public_exponent)?,
})?)
}
}
Expand All @@ -157,7 +169,7 @@ impl pkcs1::EncodeRsaPublicKey for PublicKey {
pub(crate) fn verify_algorithm_id(algorithm: &spki::AlgorithmIdentifierRef) -> spki::Result<()> {
match algorithm.oid {
pkcs1::ALGORITHM_OID => {
if algorithm.parameters_any()? != pkcs8::der::asn1::Null.into() {
if algorithm.parameters_any()? != asn1::Null.into() {
return Err(spki::Error::KeyMalformed);
}
}
Expand Down Expand Up @@ -205,7 +217,7 @@ impl EncodePrivateKey for PrivateKey {

pkcs8::PrivateKeyInfoRef::new(
pkcs1::ALGORITHM_ID,
OctetStringRef::new(private_key.as_bytes())?,
asn1::OctetStringRef::new(private_key.as_bytes())?,
)
.try_into()
}
Expand All @@ -218,10 +230,7 @@ impl EncodePublicKey for PublicKey {

pkcs8::SubjectPublicKeyInfoRef {
algorithm: pkcs1::ALGORITHM_ID,
subject_public_key: pkcs8::der::asn1::BitStringRef::new(
0,
subject_public_key.as_ref(),
)?,
subject_public_key: asn1::BitStringRef::new(0, subject_public_key.as_ref())?,
}
.try_into()
}
Expand Down
Loading