implicitly;  indirectly;  tacitly;  by implication;  obscurely
 memorization;  memorisation;  learning by heart
 secret manoeuvres (maneuvers);  operating behind the scenes
 suspicion will raise bogies;  once you suspect something, everything else will look suspicious;  jumping at shadows
 (theatrical) blackout;  taking a (sudden) turn for the worse;  rapid deterioration
 dark side (of nature, town, etc.)
 dark clouds;  threatening signs;  ominous indications
 tacit;  unspoken;  implicit
 tacit understanding;  unspoken agreement
 dark;  gloomy;  somber;  depressing
 personal identification number;  PIN;  password number
 encryption;  encipherment;  password protection
 recitation;  reciting from memory
 light and darkness;  light and shade
 autosuggestion;  self-suggestion
 Dark Continent (i.e. Africa)
 rote memorization (memorisation);  rote learning;  indiscriminate memorizing (memorising)
 secret feud;  wordless pantomime performed in the dark (in kabuki)
 imbecility;  feeblemindedness;  dark
 reef;  sunken rock;  unforeseen difficulty
 the dark side;  the seamy side
 to run aground;  to strike a rock;  to be stranded on a reef;  to reach a deadlock;  to come to a standstill;  to run into difficulties
 dark;  gloomy;  black;  doleful;  discouraged;  disappointed
 dark clouds gather;  threatening signs emerge;  trouble is afoot
 subterranean drain;  culvert;  conduit
 to decide the outcome (e.g. game);  to be very different;  to be sharply contrasted
 night-vision scope;  night scope
 groping in the dark;  exploring new avenues without having any clues
 dark place;  unlit spot;  darkness
 memorizing a musical score
 assassination of U.S. President John F. Kennedy (November 22, 1963);  JFK assassination
 memorization power;  ability to remember;  (good) memory
 eclipse period (in viral lifecycle);  eclipse phase;  dark age
 secretly;  covertly;  tacitly
 cryptographic key;  encryption key
 nyctophobia;  fear of the dark;  scotophobia
 gloom;  darkness;  seclusion
 camera obscura;  black box
 a work or subject to be memorized (memorised)
 butoh;  style of contemporary Japanese dance featuring dancers in white paint
 encrypted mail;  cyphermail
 tacit knowledge (knowledge management terminology)
 encryption key;  cryptographic key
 cryptographic system;  cryptosystem
 behind-the-scenes maneuvering;  behind-the-scenes manoeuvering;  secret maneuvers;  secret manoeuvres
 cryptography;  encryption technology
 dead of night;  shades of night;  black of night
 declaring a concealed kong;  forming a concealed four-of-a-kind
 beautiful scenery of spring;  red-light district
 sad thought;  depressing reflection
 suspicion begets monsters
 cryptography;  cryptographic theory
 assassination of U.S. President John F. Kennedy (November 22, 1963);  JFK assassination
 scent of a flower floating about in the air;  lingering scent of a flower in the darkness
 secret language;  code word;  argot
 secretly;  covertly;  tacitly
 gathering dark clouds;  being under the shadow of
 crypto-assets;  cryptocurrency assets
 dark figure (esp. of crime);  dark number;  hidden figure;  difference between the actual and reported figure
 symmetric key cryptography
 secret key cryptography;  symmetric key cryptography
 road taken by a Chinese ajari buddhist monk when he incurred the wrath of emperor Genso (685-762)
 dark hole;  idiot;  fool;  historical road
 Great Dark Spot (on Neptune)
 cryptography;  cryptographic technique
 concealed pung;  concealed three-of-a-kind
 body part encryption indication
 (both) the bright and dark sides
 scotopic vision;  twilight vision
 conventional cryptosystem
 implicit link (process definition)
 cryptographic synchronization
 implicit link (process definition)
 encryption;  coding;  password
 conventional cryptosystem
 link-by-link encipherment
 symmetric key cryptography
 Data Encryption Standard;  DES
 indiscriminate learning by heart
 symmetric key cryptography
 implicit scope terminator
 giving an amorous sidelong look;  casting an amorous glance (at);  playing up to someone behind the scenes
 pairing-based cryptography
 subterranean drain;  culvert;  conduit