Crypto¶

Cryptanalysis¶

Kerckhoff's Principle
Classical Cryptanalysis
- Mathmatical Analysis
- Brute-Force Attacks
  - Substitution Cipher
    
    Caesar Cipher
    - Exhaustive Key Search
    - Letter Frequency Analysis
    - Implementation Attacks
    - Social Engineering

Symmetric Cipher¶

Stream Cipher

encrypt bits individually

usually small and fast

security dependes entirely on key stream (sync, async), which is random and reproducible
- vulnerable to reused key attack
```
E(A) = A xor C
E(B) = B xor C
E(A) xor E(B) = A xor B
```
- key stream generator
  
  the key stream generator works like a Pseudorandom Number Generator (RNG), which generate sequences from initial seed (key) value
  
  $s_0 = seed, s_{i+1} = f(s_i, s_{i-1}, ..., s_{i-t})$
  - Linear Congruential Generator (LCG)
    
    $S_0 = seed, S_{i+1} = AS_i + B\ mod\ m$
    
    Assume
    - unknown A, B and S0 as key
    - m = 2^32
    - S1, S2, S3 are known
    Solving
    - $S_2 = AS_1 + B\ (mod\ m)$
    - $S_3 = AS_2 + B\ (mod\ m)$
    Answer
    - $A = (S_2 - S_3) \times inverse(S_1 - S_2, m)\ (mod\ m)$
    - $B = (S_2 - AS_1)\ (mod\ m)$
  - MT19937
    
    python's default RNG
    - can be recovered by 32x624 consecutive bits
      - from randcrack import RandCrack
  - Lineare Feedback Shift Register (LFSR)
    
    $S_{i+3} = S_{i+1} \oplus S_{i}$
    - Characteristic Polynomial
      - $P(x) = x^m + p_{m-1}x^{m-1} + ... + p_1x + p_0$
Block Cipher > - always encrypt a full block (several bits) > - common for internet applications

OpenSSL¶

Generate

Generate cert chain
SAN
/etc/ssl/openssl.cnf

Self-signed Certificate (Root CA)

#CA
openssl genrsa -out ca.key 4096
openssl req -new -out ca.csr -sha256 \
    -key ca.key -nodes \
    -subj "/C=TW/ST=Taiwan/L=Hsinchu/O=Organization/OU=Organization Unit/CN=Common Name"

openssl ca -selfsign -keyfile ca.key -in ca.csr -outdir . -out ca.crt \
    -startdate 20211001000000Z -enddate 20311001000000Z -config <(cat <<-EOF
[ ca ]
default_ca                   = CA_default

[ CA_default ]
database                     = ./index.txt
email_in_dn                  = no
rand_serial                  = yes
default_md                   = sha256
default_days                 = 730
policy                       = policy_any

[ policy_any ]
countryName                  = supplied
stateOrProvinceName          = optional
organizationName             = optional
organizationalUnitName       = optional
commonName                   = supplied
emailAddress                 = optional

EOF
)

#CA in one command
openssl req -new -sha256 -x509 -days 3650 -out ca.crt \
    -newkey rsa:4096 -nodes -keyout ca.key \
    -subj "/C=TW/ST=Taiwan/L=Hsinchu/O=Organization/OU=Organization Unit/CN=Common Name" \
    -addext "subjectAltName=DNS:example.com"

Sign certificate

#CSR
openssl req -new -out intermediate.csr -sha256 \
    -newkey rsa:4096 -nodes -keyout intermediate.key \
    -subj "/C=TW/ST=Taiwan/L=Hsinchu/O=Organization/OU=Organization Unit/CN=Common Name" \
    -config <(cat <<EOF
[ req ]
...
EOF
)

#CRT
openssl x509 -req -out intermediate.crt -in intermediate.csr -days 7300 \
    -CA ca.crt -CAkey ca.key -CAserial ca.serial -CAcreateserial \
    -extensions x509v3_config -extfile <(cat <<EOF
[ x509v3_config ]
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = CA:true, pathlen:0
EOF
)

Sign CRL

#CRL
openssl ca -gencrl -keyfile ca.key --cert ca.crt -out crl.pem \
    -crlexts crl_ext --crldays 730 -revoke ${CRT_PATH} -config <(cat <<EOF
[ ca ]
default_ca                   = CA_default

[ CA_default ]
database                     = ./index.txt
default_md                   = sha256

[ crl_ext ]
authorityKeyIdentifier       = keyid:always,issuer:always
EOF
)

Sign Binary

set -e

readonly dir=demoCA
readonly revoke_server=${1:?revoke server}

mkdir ${dir}
touch ${dir}/index.txt
openssl rand -hex 16 > ${dir}/serial
openssl rand -hex 16 > ${dir}/crlnumber

openssl req -new -out ca.csr -sha256 \
  -newkey rsa:4096 -keyout ca.key -nodes \
  -subj "/C=TW/ST=Taiwan/L=Hsinchu/O=Organization/OU=Organization Unit/CN=Test CA"

openssl req -new -out codesign.csr -sha256 \
  -newkey rsa:4096 -keyout codesign.key -nodes \
  -subj "/C=TW/ST=Taiwan/L=Hsinchu/O=Organization/OU=Organization Unit/CN=Test Code Signing"

openssl ca -selfsign -cert ca.crt -keyfile ca.key -in ca.csr -outdir . -out ca.crt \
  -startdate 20200101000000Z -enddate 20300101000000Z \
  -extensions x509v3_config -extfile <(cat <<EOF
[ x509v3_config  ]
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical,CA:true, pathlen:0
crlDistributionPoints = URI:http://${revoke_server}/ca.crl
EOF
)

openssl ca -cert ca.crt -keyfile ca.key -in codesign.csr -outdir . -out codesign.crt \
  -startdate 20200101000000Z -enddate 20300101000000Z \
  -extensions x509v3_config -extfile <(cat <<EOF
[ x509v3_config  ]
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical,CA:false, pathlen:0
keyUsage = critical,digitalSignature
extendedKeyUsage = codeSigning
crlDistributionPoints = URI:http://${revoke_server}/ca.crl
EOF
)

openssl pkcs12 -export -passout pass: -out codesign.pfx -inkey codesign.key -in codesign.crt -certfile ca.crt
# openssl ca -revoke ${crt:?cert to revoke} -cert ca.crt -keyfile ca.key
openssl ca -gencrl -cert ca.crt -keyfile ca.key -out ca.crl

$cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2
$cert.Import("C:\Users\user\Desktop\codesign.pfx", $null, "Exportable,PersistKeySet")
Set-AuthenticodeSignature -FilePath "C:\Users\user\Desktop\xvrshell.exe" -Certificate $cert

Verify

Cert Chain

openssl verify -CAfile root.crt -untrusted intermediate.crt product.crt
openssl verify -CAfile <(cat intermediate.crt root.crt) product.crt

openssl verify -crl_check -CAfile <(cat ca.crt crl.pem) intermediate.crt

Cert Pair

printf '123' \
    | openssl rsautl -encrypt -inkey <(openssl x509 -pubkey -noout -in sensor.crt) -pubin \
    | openssl rsautl -decrypt -inkey sensor.key

CRL

openssl s_client \
    -CAfile <(cat ca.crt crl.pem) \
    -crl_check -connect 127.0.0.1:12345 \

Read cert

openssl x509 -in product.crt -noout -text

TLS Server / Client

Basic

openssl s_server -key server.key -cert server.crt [-accept <ip>:<port>]
openssl s_client [-showcerts] -connect <ip>:<port>

Verify Server

openssl s_server [-debug] \
    -CAfile root.crt \
    -cert_chain <(cat product.crt intermediate.crt) \
    -cert server.crt -key server.key \
    [-accept <ip>:<port>]

openssl s_client [-showcerts] \
    -CAfile root.crt \
    -verify_return_error \
    -connect <ip>:<port>

Mutual Auth

#Server Alternative 1
openssl s_server [-debug] \
    -CAfile root.crt \
    -cert_chain <(cat product.crt intermediate.crt) \
    -cert server.crt -key server.key \
    -verify_return_error -Verify 5 \
    [-accept <ip>:<port>]

#Server Alternative 2
socat "OPENSSL-LISTEN:8888,cafile=root.crt,certificate=client-chain.crt,key=client.key,reuseaddr,verify" STDOUT

#Client Alternative 1
openssl s_client [-showcerts] \
    -CAfile root.crt \
    -cert_chain <(cat product.crt intermediate.crt) \
    -cert client.crt -key client.key \
    -verify_return_error \
    -connect <ip>:<port>

#Client Alternative 2
curl \
    --cacert root.crt \
    --cert <(cat client.crt product.crt intermediate.crt) \
    --key client.key \
    --resolve <Cert CN>:<port>:<ip>
    https://<Cert CN>:<port>

S/MIME data signing

$ openssl smime -sign -binary -signer cert.pem -inkey key.pem -outform DER -md sha256 -out sigature -in ${filename:?} -nocerts
$ openssl smime -verify -in sig -inform DER -content ${filename:?} -noverify -out /dev/null

MakeCert and New-SelfSignedcertificate

# MakeCert -n 'CN=code.signing' -ss My -r -pe -sr localmachine -cy end -eku 1.3.6.1.5.5.7.3.3 -len 4096 -b 2020/01/01 -e 2025/01/01
New-SelfSignedCertificate -CertStoreLocation 'Cert:\CurrentUser\My' -KeyAlgorithm RSA -KeyLength 4096 -Type CodeSigningCert -KeyUsage DigitalSignature -KeyUsageProperty Sign -Subject 'CN=code signing test'
Set-AuthenticodeSignature -FilePath @(Get-ChildItem -Recurse '*.exe','*.dll','*.ps1') -Certificate (Get-ChildItem Cert:\CurrentUser\My -codesigning)[0] -IncludeChain 'NotRoot' -HashAlgorithm SHA256 -TimestampServer 'http://timestamp.globalsign.com/?signature=sha2'
signtool.exe verify /pa <binary>

Signed Certificate Timestamp (SCT)
- Signed Certificate Timestamp (SCT) Validation | Google