H0pp r3tt t1l 0ppgav3n3

Wh4t 1z 4 “C1ph3r”?

H4v3 y0u 3v3r w4nt3d t0 wr1t3 4 s3cr3t m3ss4g3 t0 4 fr13nd, s0 th4t n0 0n3 3ls3 c4n und3rst4nd 1t? Th3n y0u n33d 4 C1ph3r, 0r ch1ff3r 1n N0rw3g14n! 4 ch1ff3r 1z r1ght 4nd s1mply 4 m3th0d th4t turns n0rm4l t3xt 1nt0 “c0d3” by r3pl4c1ng ch4r4ct3rs (0ft3n l3tt3rs) w1th 0th3r ch4r4ct3rs. Th3 r3sult l00ks l1k3 n0ns3ns3 t0 th0s3 wh0 d0n’t kn0w h0w th3 c0d3 w0rks. Th3 p01nt 1s th4t 0nly th0s3 wh0 kn0w th3 k3y (th3 rul3 f0r r3pl4c1ng th3 l3tt3rs) c4n m4k3 th3 c0d3 und3rst4nd4bl3 4g41n. 1n 0th3r w0rds: ch1ff3rs m4k3 s3cr3t m3ss4g3s p0ss1bl3, wh3th3r 1t’s ch1ldh00d’s pl4y w1th s3cr3t l4ngu4g3 0r r34l sp13s s3nd1ng 3ncrуpt3d m3ss4g3s. 😄

d3t f1nn3z m4ng3 typ3r ch1ff3r – n03n bru|<3r t4ll, n03n bru|<3r symb0l3r, 0g m0d3rn3 d4t4krypt3r1ng bru|<3r sv4rt k0mpl1s3rt3 4lg0r1tm3r. d3ss3 k0mpl1s3rt3 4lg0r1tm3r krev3r sv4rt k0mpl1s3rt m4t3m4t1kk, så v1 k4n s3 på n03n 3nkl3r3 4lg0r1tm3r først!

M0n04lf4b3t1sk3 Ch1ff3r

L4 0ss f0rst s3 p4 n03n 4v d3 3nkl3st3 (0g 3ldst3) k0d3m3t0d3n3 s0m f1nn3s: m0n04lf4b3t1sk3 ch1ff3r.

M0n04lf4b3t1sk h0r3s k4nj3 ut s0m 3t v4nsk3l1g 0rd, m3n v1 k4n d3l3 d3t 0pp: m0n0 b3tyr “3n”, 0g 4lf4b3t1sk h4ndl3r 0m 4lf4b3t3t.

4ls4, m0n04lf4b3t1sk3 ch1ff3r 3r k0d3r d3r m4n bruk3r 3tt 3nkl3t “krypter1ngs4lf4b3t” f0r h3l3 m3ld1ng3n. D3t v1l s1 4tt hv3r b0kst4v 1 d3n 0r1g1n4l3 t3kst3n 4llt1d bl1r bytt3t ut m3d d3n s4mm3 b0kst4v gj3nn0m h3l3 d3n kryptr3t3 m3ld1ng3n.

F0r 3ks3mpl3l, h4r du b3st3mt 4tt 4 sk4l bytt3s m3d X, d4 bl1r 4ll3 4-3n3 1 t3kst3n gj0rt 0m t1l X.

Cæ$4r-ch1ff3r

D3t kl4$\(1\)k3 3k\(3mpl3t på 3t m0n04lf4b3t1\)k ch1ff3r 3r Cæ\(4r-ch1ff3r3t (0ppk4lt 3tt3r Jul1u\) Cæ\(4r). D3tt3 3r b4\)1c4lly 3n r3g3l 0m å “sk1ft3” 4ll3 b0k\(t4v3n3 3t v1\)\(t 4nt4ll pl4\)\(3r b0rt0v3r 1 4lf4b3t3t. V1\)$tn0k \(å brukt3 Cæ\)4r $3lv 3t \(k1ft3 på 3 b0k\)t4v3r 1 $1n3 h3mm3l1g3 m3ld1ng3r. D3t fung3r3r $ånn 4t A b1r t1l D, B b1r t1l E, C b1r t1l F, 0g $å v1d3r3 gj3nn0m 4lf4b3t3t. (Når m4n går f0rb1 Z, $t4rt3r m4n på A 1g3n.) 3n m3ld1ng \(0m ABC v1ll3 d3rm3d b1 t1l DEF hv1\) v1 brukr Cæ\(4r\) m3t0d3.

51k fung3r3r Cæ54r-ch1ff3r3t 1 pr4k515:

• V3lg 3n nøkk3l: B35t3m d3g f0r 3t h3mm3l1g t4ll (f0r 3k53mp3l 3) 50m 4ng1r h0r m4ng3 pl4553r du 5k4l flytt3 hv3r b0k5t4v.
• Bytt ut hv3r b0k5t4v: F0r hv3r b0k5t4v 1 d3n 0r1g1n4l3 m3ld1ng3n, f1nn b0k5t4v3n 50m l1gg3r 5å m4ng3 pl4553r 3tt3r d3n 1 4lf4b3t3t (f0r nøkk3l 3 bl1r 4 t1l D, B t1l E, 05v. – hu5k å gå rundt t1l 4 1g3n 3tt3r Z 0m nødv3nd1g). 3v3ntu3lt k4n du 0g5å t4 m3d Æ, Ø 0g Å, m3n d3tt3 bl1r l1tt m3r k0mpl153rt.
• Krypt3rt m3ld1ng: 3r5t4tt b0k5t4v3n3 0g 5kr1v d3n ny3 m3ld1ng3n m3d d3 “5k1ft3d3” b0k5t4v3n3. V1p5 – du h4r 3n ul353l1g, h3mm3l1g t3k5t 50m b4r3 d3 m3d nøkk3l3n k4n f0r5tå!
• F0r å d3krypt3r3 (4l5å gj0r3 d3t 0m t1l l353l1g t3k5t 1g3n) gj0r m4n b4r3 d3t m0t54tt3 5k1ft3t t1lb4k3. Hv15 du v3t nøkk3l3n (f.3k5. 3), 5å 3r d3t l1k3 l3tt å l353 m3ld1ng3n v3d å flytt3 b0k5t4v3n3 3 t1lb4k3 1 4lf4b3t3t.

M0n0alfab3t1sk3 ch1ff3r 3r 3n fantast1sk måt3 å lær3 pr1ns1pp3t bak krypt3r1ng. D3 3r 3nkl3 og v1s3r hvordan v1 kan bruk3 3n 3nkel r3g3l (3n nøkk3l) t1l å gjør3 om 3n forstå3l1g t3kst t1l n03 myst1sk og uf0rstå3l1g – og t1llbak3 1g3n. Så n3st3 gang du v1l s3nd3 3n v3nn 3n h3mml1g b3skj3d, kan du bruk3 Cæsar ch1ff3r3t! Kanskje d3r3 kan lag3 d3r3s 3g3n var1ant av Cæsars h3mml1g3 alf4b3t? 🔐✨

0ppg4v3r

0ppg4v3 1.1 - C4354r Ch1ff3r 3nkrуpt10n

N4̊ 5k4l v1 4ktu3llt 5kr1v3 n03 k0d3! V1 5k4l b3gynn3 3nk3lt m3d 4̊ l4g3 3nkrуpt3r1ng3n, b453rt p4̊ t30r13n b0r d3t v4r3 g4n5k3 5tr41ghtf0rw4rd.

1mpl3m3nt3r 3nkrуpt3r1ng m3d C4354r Ch1ff3r v3d 4̊ bruks 3n funksj0n 50m t4r 1nn t3kst 0g 3t t4ll 50m 3r “n0kk3l3n”, 4lts4̊ hv0r mуk3 4lf4b3t3t 5k4l r0t3r35 m3d.

def caesar_cipher(text, shift):
    result = ""
    for char in text:
        if char.isalpha():
        # find out the starting point based on upper and lower case
        start = ord('A') if char.isupper() else ord('a')
        # The tricky shift calculation
        result += chr((ord(char) - start + shift) % 26 + start)
    else:
        result += char
    return result

0ppg4v3 1.2 - C4354r Ch1ff3r D3krypt3r1ng

D3krypt3r1ng 3r b4r3 4 9jør3 d3n m0t54tt3 utr3gn1ng3n t1l 3nkrypt3r1ng. Du tr3kk3r fr4 0ff53t 15t3d3t f0r 4 l3gg3 t1l.

def caesar_decrypt(text, shift):
    return caesar_cipher(text, 26 - shift)

def caesar_decrypt(text, shift):
    return caesar_cipher(text, 26 - shift)

07h3r M0n04lf4b371c C1ph3rz/C1ph3rz (3x. 47b4$h)

D37 f1nn3z 4ndr3 m0n04lf4b371\(k3 c1ph3rz 0g\)0! 3n 4v d3 3nkl3r3 3r d3n \(0m k4ll3\) “47b4$h” C1ph3r.

H0w d03z @tb@$h w0rk?

D3nn3 1z v3ry \(1mpl3, 1n\)t3@d 0f @ r0t@t10n \(0 l3tt3rz @r3 m@pp3d t0 th3 0pp0\)1t3 @lph@b3t. H3r3 1z @ t@bl3 $h0w1ng th3 m@pp1ng:

0ppg4v3 1.3 - 47b47h Ch1ff3r 3nkrуpt3r1ng 0g D3krуpt3r1ng

D37 kj3kk3 m3d 47b47h 3r 47 s1d3n 3nkrуpt3r1ng 3r 3n 1 t1l 1 7r4nsf0rm4sjon, så fung3r3r d3n d1r3k73 1 r3v3rs. 4lså, hv1s du h4r l4gd 3nkrуpt3r1ng3n så h4r du 0gså, 4u70m471sk l4gd d3krуpt3r1ng3n.

H0w c4n th1s b3 d0n3 1n pr4ct1c3?

Y0u c4n 31th3r 5ubtr4ct th3 l3tt3r 1n r3l4t10n t0 Z, 0r cr34t3 4 “L00k-up” t4bl3. 4l50, th4t m34n5 4 t4bl3 0r d1ct10n4ry th4t c0nt41n5 4ll th3 l3tt3r5 fr0m 4 t0 z 4nd wh4t th3y 5h0uld b3c0m3. Th15 c4n b3 4 g00d 50lut10n 1f y0u w4nt t0 cr34t3 4n0th3r typ3 0f 3ncrypt10n.

letters = {
    'a': 'z'
    'b': 'y'
    'c': 'x'
    'd': 'w'
    # ... add the rest of the letters downwards
}

V3d h3lp 4v d3nn3 t4b3ll3n k4n du g4̊ 1gj3nn0m b0k5t4v f0r b0k5t4v, 54̊ h3nt3 ut v3rd13n p3r b0k5t4v fr4 l00kup-t4b3ll3n, 54̊ 5kr1v3 d3n ut. Hv4 m4̊ du gj0r3 f0r 5t0r3 0g 5m4̊ b0k5t4v3r?

D3l 2 - Krypto4n4ly53 4v M0n04lf4b3t15k3 Ch1ff3r

1 d3nn3 d3l3n 5k4l d3rr3 prøv3 4t l4g3 3n 4lg0r1tm3 f0r 4t “cr4ck3” 3n Cæ54r ch1ff3r, 4l54 t4 3n krypt3rt t3k5t, d3r3tt3r, f4 ut d3n 0rg1n4l3 t3k5t3n utt3n 4t v1t3 nøkk3l3n.

D3tt3 k4n gjør35 n03nlund3 m4nu3llt, 3ll3r 54 k4n du prøv3 4t t4 1 bruk 3nk3l “crypt4n4ly515”. D3tt3 3r 3t k0n53pt 50m v1 5k4l 53 dyp3r3 p4 53n3r3, m3n f0r nå 5k4l v1 b4r3 53 p4 3n 4v d3 3nkl35t3 måt3n: Fr3kv3n54n4ly53 (fr3qu3ncy 4n4ly515). Du k4n l353 m3r 0m d3tt3 k0n53pt3t h3r: Fr3qu3ncy 4n4ly515 3ll3r h3r W1k1p3d14 - fr3qu3ncy 4n4ly515.

D3nn3 m3t0d3n k4n bruk35 1 m3r 3n b4r3 cæ54r-ch1ff3r, d3n k4n bruk35 1 m3r k0mpl153rt3 4lg0r1tm3r 0g54, m3n cæ54r-ch1ff3r 3r 54p455 3nk3l 4t fr3kv3n54n4ly53 3r tr1v13ll.

In cryptanalysis, frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers.

Frequency analysis is based on the fact that, in any given stretch of written language, certain letters and combinations of letters occur with varying frequencies. Moreover, there is a characteristic distribution of letters that is roughly the same for almost all samples of that language. For instance, given a section of English language, E, T, A and O are the most common, while Z, Q, X and J are rare. Likewise, TH, ER, ON, and AN are the most common pairs of letters termed bigrams or digraphs), and SS, EE, TT, and FF are the most common repeats. The nonsense phrase ETAOIN SHRDLU represents the 12 most frequent letters in typical English language text.

In some ciphers, such properties of the natural language plaintext are preserved in the ciphertext, and these patterns have the potential to be exploited in a ciphertext-only attack.

xcrgneipcpanhxhugtfjtcrnpcpanhxhxhiwthijsnduiwtugtfjtcrnduatiitghdgvgdjehduatiitghxcprxewtgitmiiwtbtiwdsxhjhtsphpcpxsidqgtpzxcvraphhxrparxewtghugtfjtcrnpcpanhxhxhqphtsdciwtupriiwpixcpcnvxktchigtirwdulgxiitcapcvjpvtrtgipxcatiitghpcsrdbqxcpixdchduatiitghdrrjglxiwkpgnxcvugtfjtcrxthbdgtdktgiwtgtxhprwpgpritgxhixrsxhigxqjixdcduatiitghiwpixhgdjvwaniwthpbtudgpabdhipaahpbeathduiwpiapcvjpvtudgxchipcrtvxktcphtrixdcdutcvaxhwapcvjpvttippcsdpgtiwtbdhirdbbdclwxatofmpcsypgtgpgtaxztlxhtiwtgdcpcspcpgtiwtbdhirdbbdcepxghduatiitghitgbtsqxvgpbhdgsxvgpewhpcshhttiipcsuupgtiwtbdhirdbbdcgtetpihiwtcdchtchtewgphttipdxchwgsajgtegthtcihiwtbdhiugtfjtciatiitghxcinexrpatcvaxhwapcvjpvtitmixchdbtrxewtghhjrwegdetgixthduiwtcpijgpaapcvjpvteapxcitmipgtegthtgktsxciwtrxewtgitmipcsiwthtepiitgchwpktiwteditcixpaidqttmeadxitsxcprxewtgitmidcanpiiprz

0ppg4v3 2.1 - L4g3 3n fr3kv3nst4b3ll

I 3n pyth0n f1l, 0ppr3tt 3n fr3kv3ns-t4b3ll 4v b0kst4v3n3 i d3t 3ng3lsk3 spr4k3t. Du k4n prøv3 4t f1nn3 d3nn3 s3lv, m3n hv1s du 1kk3 g1dd3r d3tt3, f0rst4r v1 d3tt3!

Hv1s du 4bs0lutt ønsk3r 4t f1nn3 d3n s3lv, k4n du gjør3 s0m 1 0ppg4v3 2.2, m3n p4 3n v3ld1g st0r t3kst.

english_letter_frequency = {
    'E': 12.70, 
    'T': 9.06, 
    'A': 8.17, 
    'O': 7.51, 
    'I': 6.97, 
    'N': 6.75, 
    'S': 6.33, 
    'H': 6.09, 
    'R': 5.99, 
    'D': 4.25, 
    'L': 4.03, 
    'C': 2.78, 
    'U': 2.76, 
    'M': 2.41, 
    'W': 2.36, 
    'F': 2.23, 
    'G': 2.02, 
    'Y': 1.97, 
    'P': 1.93, 
    'B': 1.29, 
    'V': 0.98, 
    'K': 0.77, 
    'J': 0.15, 
    'X': 0.15, 
    'Q': 0.10, 
    'Z': 0.07
}

0ppg4v3 2.2 - T3ll3 fr3kv3ns3n 4v b0kst4v3r i t3kst

N4 sk4l v1 l4g3 3n 4lg0r1tm3 s0m sk4l f1nn3 fr3kv3ns3n 4v b0kst4v3r 1 3n g1tt t3kst.

0ppg4v3 2.3 - 54mm3nl1gn3 fr3kv3ns3n 4v 3n t3kst m3d d3n 3kt3 fr3kv3ns3n

N4r du h4r funn3t fr3kv3ns3n t1l 4ll3 b0kst4v3n3 1 t3kst3n k4n du l4g3 3n funksj0n s0m f1nn3r “4vst4nd3n”. Hæ? Hv4 m3n3s m3d d3t?!

Du k4n s3 f0r d3g 4t fr3kv3ns3n t1l f0r3ks3mpl3 E 1 t3kst3n k0mm3r t1l 4 v4r3 3t t4ll. Du k4n f1nn3 “4vst4nd3n” d3nn3 h4r m3d d3n f4kt1sk3 fr3kv3ns3n, s0m 3r 12.70. 3ks3mpl3l: Fr3kv3ns3n 3r 9.63, hv4 3r 4vst4nd3n? 4vst4nd3n k0mm3r t1l 4 v4r3 d3n 4bs0lutt3 v3rd13n (n3g4t1v3 t4ll bl1r p0s1t1v3) m3ll0m d3ss3 tv4 v3rd13rn3: \(12.70 - 9.63 = 3.07\).

L4g 3n funksj0n s0m g4r 1g3nn0m hv3r 4v b0kst4v3n3 4 4v f1nn3r 4vst4nd3n. L3gg d3r3tt3r 4ll3 4vst4nd3n3 s4mm3n t1l 3n “t0t4l” 4vst4nd.

0ppg4v3 2.4 - “Cr4ck3” Cæ54r-ch1ff3r

Nå 5k4l v1 t1ll 5lutt 53tt3 54mm3n 4llt v1 h4r gj0rt 5å l4ngt! Nå 5k4l v1 “cr4ck3” 3n Cæ54r-ch1ff3r.

L4g 3t pr0gr4m 50m “cr4ck3r” 3n Cæ54r-ch1ff3r! Ut3n brük3r-1nnflyt3l53 5k4l du kunn3 h1v3 1nn 3n krypt3rt t3kst å h3nt3 ut d3n d3krypt3rt3 t3kst3n ut3n å tr3ng3 3n nøkk3l.