diff --git a/book/source/18-zoom_certificates.md b/book/source/18-zoom_certificates.md
index b74ffa9..3492d4f 100644
--- a/book/source/18-zoom_certificates.md
+++ b/book/source/18-zoom_certificates.md
@@ -169,7 +169,7 @@ The packet type ID ("6") defines the semantics of the following data within the
 
 - `ed25519_public`: This is the [algorithm-specific representation](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-algorithm-specific-part-for-ed2) of the public key material. The format is based on the value of `pk_algo`, which, in this case, is 32 bytes of Ed25519 public key data.
 
-[^CTB]: Sequoia uses the term CTB (Cipher Type Byte) to refer to the RFC's [packet type ID](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-packet-headers). In earlier RFC versions, this field was known as the "Packet Tag."
+[^CTB]: Sequoia uses the term CTB ({term}`Cipher Type Byte`) to refer to the [packet type ID](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-packet-headers).
 
 Note that the *Public-Key packet* contains only the public part of the key.
 
diff --git a/book/source/19-zoom_private_keys.md b/book/source/19-zoom_private_keys.md
index 34a2fb8..aa55029 100644
--- a/book/source/19-zoom_private_keys.md
+++ b/book/source/19-zoom_private_keys.md
@@ -64,7 +64,7 @@ The Secret-Key packet consists in large part of the actual cryptographic key dat
 - `CTB: 0xc5`[^CTB]: The [packet type ID](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-packet-headers) for this packet. The binary representation of the value `0xc5` is `11000101`. Bits 7 and 6 show that the packet is in *OpenPGP packet format* (as opposed to in *Legacy packet format*). The remaining 6 bits encode the type ID's value: "5". This is the value for a Secret-Key packet, as shown in the list of [packet type IDs](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-packet-types).
 - `length: 0x4b`: The remaining length of this packet.
 
-[^CTB]: Sequoia uses the term CTB (Cipher Type Byte) to refer to the RFC's [packet type ID](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-packet-headers). In previous versions, the RFC called this field "Packet Tag".
+[^CTB]: Sequoia uses the term CTB ({term}`Cipher Type Byte`) to refer to the [packet type ID](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-packet-headers).
 
 The packet type id defines the semantics of the remaining data in the packet. We're looking at a Secret-Key packet, which is a kind of [Key Material Packet](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-key-material-packets).