target = "https://www.rfc-editor.org/rfc/rfc9000#section-17.3.1"

# 17.3.1.  1-RTT Packet
#
# A 1-RTT packet uses a short packet header.  It is used after the
# version and 1-RTT keys are negotiated.
# 
# 1-RTT Packet {
#   Header Form (1) = 0,
#   Fixed Bit (1) = 1,
#   Spin Bit (1),
#   Reserved Bits (2),
#   Key Phase (1),
#   Packet Number Length (2),
#   Destination Connection ID (0..160),
#   Packet Number (8..32),
#   Packet Payload (8..),
# }
# 
#                        Figure 19: 1-RTT Packet
# 
# 1-RTT packets contain the following fields:
# 
# Header Form:  The most significant bit (0x80) of byte 0 is set to 0
#    for the short header.
# 
# Fixed Bit:  The next bit (0x40) of byte 0 is set to 1.  Packets
#    containing a zero value for this bit are not valid packets in this
#    version and MUST be discarded.  A value of 1 for this bit allows
#    QUIC to coexist with other protocols; see [RFC7983].
# 
# Spin Bit:  The third most significant bit (0x20) of byte 0 is the
#    latency spin bit, set as described in Section 17.4.
# 
# Reserved Bits:  The next two bits (those with a mask of 0x18) of byte
#    0 are reserved.  These bits are protected using header protection;
#    see Section 5.4 of [QUIC-TLS].  The value included prior to
#    protection MUST be set to 0.  An endpoint MUST treat receipt of a
#    packet that has a non-zero value for these bits, after removing
#    both packet and header protection, as a connection error of type
#    PROTOCOL_VIOLATION.  Discarding such a packet after only removing
#    header protection can expose the endpoint to attacks; see
#    Section 9.5 of [QUIC-TLS].
# 
# Key Phase:  The next bit (0x04) of byte 0 indicates the key phase,
#    which allows a recipient of a packet to identify the packet
#    protection keys that are used to protect the packet.  See
#    [QUIC-TLS] for details.  This bit is protected using header
#    protection; see Section 5.4 of [QUIC-TLS].
# 
# Packet Number Length:  The least significant two bits (those with a
#    mask of 0x03) of byte 0 contain the length of the Packet Number
#    field, encoded as an unsigned two-bit integer that is one less
#    than the length of the Packet Number field in bytes.  That is, the
#    length of the Packet Number field is the value of this field plus
#    one.  These bits are protected using header protection; see
#    Section 5.4 of [QUIC-TLS].
# 
# Destination Connection ID:  The Destination Connection ID is a
#    connection ID that is chosen by the intended recipient of the
#    packet.  See Section 5.1 for more details.
# 
# Packet Number:  The Packet Number field is 1 to 4 bytes long.  The
#    packet number is protected using header protection; see
#    Section 5.4 of [QUIC-TLS].  The length of the Packet Number field
#    is encoded in Packet Number Length field.  See Section 17.1 for
#    details.
# 
# Packet Payload:  1-RTT packets always include a 1-RTT protected
#    payload.
# 
# The header form bit and the Destination Connection ID field of a
# short header packet are version independent.  The remaining fields
# are specific to the selected QUIC version.  See [QUIC-INVARIANTS] for
# details on how packets from different versions of QUIC are
# interpreted.

[[spec]]
level = "MUST"
quote = '''
Packets
containing a zero value for this bit are not valid packets in this
version and MUST be discarded.
'''

[[spec]]
level = "MUST"
quote = '''
The value included prior to
protection MUST be set to 0.
'''

[[spec]]
level = "MUST"
quote = '''
An endpoint MUST treat receipt of a
packet that has a non-zero value for these bits, after removing
both packet and header protection, as a connection error of type
PROTOCOL_VIOLATION.
'''