HKIE Professional Assessment - Information Discipline cheat sheet

Nyquist–Shannon sampling theorem: a bandlimited signal with maximum frequency f_max is fully reconstructable from samples taken at f_s > 2·f_max; f_s = 2·f_max is the Nyquist rate and practical systems oversample to relax anti-alias filter roll-off.

Shannon–Hartley capacity for an AWGN channel: C = B·log2(1 + S/N) bits/s, where B is bandwidth in Hz and S/N is the linear (not dB) signal-to-noise ratio; SNR_dB = 10·log10(S/N).

Link budget in dB form: P_rx = P_tx + G_tx + G_rx − L_path − L_misc; free-space path loss L_fs(dB) = 32.45 + 20·log10(f_MHz) + 20·log10(d_km).

Reliability block diagram rules: series elements multiply availability (A_total = ΠA_i); parallel redundant elements give A_total = 1 − Π(1 − A_i); MTBF = 1/λ and availability A = MTBF/(MTBF + MTTR).

Error-detection/correction decision rule: CRC and parity detect but do not correct; Hamming distance d_min allows detection of (d_min − 1) errors and correction of ⌊(d_min − 1)/2⌋ errors.

Data centre redundancy: N+1 tolerates one unit failure; 2N gives full mirrored capacity; 2(N+1) gives mirrored capacity plus one spare per side - tier level is set by the weakest concurrent-maintainable path.

Structured cabling limits: balanced twisted-pair horizontal channel 100 m (90 m permanent link + 10 m patch cords); fibre backbone distances depend on transceiver type (e.g. 1000BASE-SX ~550 m on OM2 multimode).

Project delivery decision rule: fixed-scope, well-understood work suits waterfall; evolving requirements with frequent stakeholder feedback suit iterative/agile; safety-critical or regulated systems require documented V-model verification and traceability.

Earned value formulas: CV = EV − AC; SV = EV − PV; CPI = EV/AC; SPI = EV/PV; EAC ≈ BAC/CPI when current cost performance is expected to persist.

CIA triad mapping: confidentiality is served by encryption and access control; integrity by hashing, MACs and digital signatures; availability by redundancy, backups and DDoS mitigation.

Symmetric vs asymmetric rule: AES (128/192/256-bit) is fast and used for bulk data; RSA/ECC is used for key exchange and signatures; hybrid schemes (e.g. TLS) encrypt the session key with asymmetric crypto and the payload with symmetric crypto.

Hash properties: SHA-256 outputs 256 bits; hashes are one-way and collision-resistant but provide no confidentiality; an HMAC adds a shared secret to a hash to give message authentication.

Key length guidance: RSA ≥ 2048 bits and ECC ≥ 256 bits are current baselines; deprecated algorithms include MD5, SHA-1 for signatures, DES/3DES and RC4.

Risk formula: risk = likelihood × impact; treatment options are avoid, reduce, transfer (insurance/contract) and accept, with residual risk formally signed off by the asset owner.

Defence in depth layers: physical, network (segmentation, firewalls, IDS/IPS), host (hardening, patching, EDR), application (input validation, secure SDLC) and data (encryption, DLP, backup).

Identity rule: authentication proves identity, authorisation grants rights, accounting records actions (AAA); MFA requires factors from at least two different categories (knowledge, possession, inherence).

Backup rule 3-2-1: at least three copies, on two different media, with one copy off-site; RPO defines tolerable data loss and RTO defines tolerable downtime - restore must be tested, not assumed.

Personal data principles (typical privacy law): lawful and fair collection, purpose limitation, data minimisation, accuracy, storage limitation, security safeguards, and breach notification within a defined statutory window.

OSI-to-TCP/IP mapping: application (OSI 5–7), transport (4), internet (3), network access (1–2); each layer adds its own header, and encapsulation reverses at the receiver.

TCP vs UDP rule: TCP gives connection-oriented, ordered, retransmitted delivery with flow and congestion control; UDP is connectionless with no delivery guarantee and is chosen for real-time voice/video and DNS queries.

IPv4 private ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16; loopback 127.0.0.0/8; link-local 169.254.0.0/16 (APIPA, indicates DHCP failure).

Subnetting: usable hosts = 2^h − 2 where h is the host-bit count; /24 gives 254 usable, /30 gives 2 usable and is used for point-to-point links; CIDR prefix length equals 32 minus host bits.

VLANs segment broadcast domains at Layer 2; inter-VLAN routing requires a Layer 3 device (router or multilayer switch); 802.1Q tags frames with a 12-bit VLAN ID (up to 4094 usable).

Wi-Fi standards: 802.11n (Wi-Fi 4) 2.4/5 GHz, 802.11ac (Wi-Fi 5) 5 GHz only, 802.11ax (Wi-Fi 6) 2.4/5/6 GHz; WPA2/WPA3 are required for enterprise security, WEP and WPA are deprecated.

DHCP DORA sequence: Discover, Offer, Request, Acknowledge; DNS resolves names to addresses via recursive and authoritative servers, with A/AAAA, CNAME, MX, TXT and PTR record types.

ITIL-style incident vs problem rule: an incident is an unplanned interruption restored by a workaround; a problem is the underlying cause investigated through root cause analysis and known-error records.

Change management rule: normal changes need CAB authorisation and a rollback plan; standard/pre-approved changes are low risk and repeatable; emergency changes are authorised after the fact with retrospective review.