# RFC Errata

Found 4 records.

## Status: Verified (1)

### RFC 8439, "ChaCha20 and Poly1305 for IETF Protocols", June 2018

Source of RFC: IRTF
Errata ID: 5689

**Status: Verified
Type: Technical
Publication Format(s) : TEXT**

Reported By: Stefan Heiss

Date Reported: 2019-04-11

Verifier Name: Colin Perkins

Date Verified: 2019-04-15

Section 2.5.1 says:

for i=1 upto ceil(msg length in bytes / 16) n = le_bytes_to_num(msg[((i-1)*16)..(i*16)] | [0x01]) a += n a = (r * a) % p end

It should say:

for i=1 upto ceil(msg length in bytes / 16) j = min(i*16-1, msg length in bytes - 1) n = le_bytes_to_num(msg[((i-1)*16)..j] | [0x01]) a += n a = (r * a) % p end

Notes:

Correction of Errata 5675

## Status: Reported (2)

### RFC 8439, "ChaCha20 and Poly1305 for IETF Protocols", June 2018

Source of RFC: IRTF
Errata ID: 5989

**Status: Reported
Type: Technical
Publication Format(s) : TEXT**

Reported By: Lê Minh Đăng

Date Reported: 2020-02-26

Section 2.4.1 says:

encrypted_message += block ^ key_stream ... encrypted_message += (block^key_stream)[0..len(plaintext)%64]

It should say:

encrypted_message |= block ^ key_stream ... encrypted_message |= (block^key_stream)[0..len(plaintext)%64]

Notes:

Because cipher text and plaint text have the same length, not length of one block so The encrypted_message must concatenation of block to block not addition.

Errata ID: 6025

**Status: Reported
Type: Technical
Publication Format(s) : TEXT**

Reported By: James Muir

Date Reported: 2020-03-21

Section 8439 says:

From Section 3 (re implementation advice for Poly1305): A constant-time but not optimal approach would be to naively implement the arithmetic operations for 288-bit integers, because even a naive implementation will not exceed 2^288 in the multiplication of (acc+block) and r.

It should say:

It is possible to create a constant-time, but not optimal, implementation by implementing arithmetic operations for 256-bit integers, because even a naive implementation will not exceed 2^256 in the multiplication of (acc+block) and r (note that we have r < 2^124 because r is "clamped").

Notes:

There are two issues 1) 288 bits is too big, and 2) a naive implementation of 288 bit integer arithmetic isn't necessarily constant time.

re #1: 288 seems to be tied to the machine int size and assumes 32-bit integers (288 is nine 32-bit integers). It is probably better to give a number independent of the machine int size.

You can compute Poly1305 using 255 bit arithmetic.

Padded blocks of the message are in the range 2^8, 2^8 +1,..., 2^129 -1.

Assuming that the partial reduction step always reduces the accumulator to 130 bits, we have acc < 2^130, so acc+block < 2^131.

r is a 16 byte value, but some of its bits are "clampled", so we have r < 2^124.

Thus (acc+block)*r < 2^255; so we can get by with 255 bit big-integer arithmetic (probably 256 bits is more convenient to work with).

re #2: big-integer arithmetic can be implemented in constant time, but perhaps not in a obvious or naive way. Keeping things constant time seems to depend on the characteristics of the underlying processor.

## Status: Rejected (1)

### RFC 8439, "ChaCha20 and Poly1305 for IETF Protocols", June 2018

Source of RFC: IRTF
Errata ID: 5675

**Status: Rejected
Type: Technical
Publication Format(s) : TEXT**

Reported By: Stefan Heiss

Date Reported: 2019-03-25

Rejected by: Colin Perkins

Date Rejected: 2019-04-15

Section 2.5.1 says:

for i=1 upto ceil(msg length in bytes / 16) n = le_bytes_to_num(msg[((i-1)*16)..(i*16)] | [0x01]) a += n a = (r * a) % p end

It should say:

for i=1 upto floor(msg length in bytes / 16) j = min(i*16-1, msg length in bytes - 1) n = le_bytes_to_num(msg[((i-1)*16)..j] | [0x01]) a += n a = (r * a) % p end

Notes:

Corection for lengths of msg blocks (full blocks are of size 16, NOT 17 and last blocks of size != 16 have to be treated separately).

--VERIFIER NOTES--

Rejected in favour of errata 5689.