Security

In this post, I will focus on the rationale behind some popular webhook security methods and will try to explain them in simple terms. 1. Basics Risks and Measures 1.1. Webhooks can be set to leak data silently Let’s assume you are a webhook provider and an attacker compromises the credentials of one of your clients. If your platform doesn’t notify users when a webhook is created or updated - the attacker can create a webhook silently and start leaking data without alerting anyone. This silent tunnel will let the attacker stay in the system longer undetected. Therefore: ...

Checking SSL certificates on a browser is easy. Just click the green lock icon and you’re good to go. But what if doing the same in a more hacker way? This is where openssl comes into play. Let’s start by checking the SSL certificate of this website: openssl s_client -connect www.serhatdundar.com:443 depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert High Assurance EV Root CA depth=1 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert SHA2 High Assurance Server CA depth=0 C = US, ST = California, L = San Francisco, O = "GitHub, Inc.", CN = www.github.com --- Certificate chain 0 s:/C=US/ST=California/L=San Francisco/O=GitHub, Inc./CN=www.github.com i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA 1 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA --- Server certificate -----BEGIN CERTIFICATE----- MIIHMDCCBhigAwIBAgIQAkk+B/qeN1otu8YdlEMPzzANBgkqhkiG9w0BAQsFADBw MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3 d3cuZGlnaWNlcnQuY29tMS8wLQYDVQQDEyZEaWdpQ2VydCBTSEEyIEhpZ2ggQXNz dXJhbmNlIFNlcnZlciBDQTAeFw0yMDA1MDYwMDAwMDBaFw0yMjA0MTQxMjAwMDBa MGoxCzAJBgNVBAYTAlVTMRMwEQYDVQQIEwpDYWxpZm9ybmlhMRYwFAYDVQQHEw1T YW4gRnJhbmNpc2NvMRUwEwYDVQQKEwxHaXRIdWIsIEluYy4xFzAVBgNVBAMTDnd3 dy5naXRodWIuY29tMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAsj49 ... -----END CERTIFICATE----- subject=/C=US/ST=California/L=San Francisco/O=GitHub, Inc./CN=www.github.com issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA --- No client certificate CA names sent Server Temp Key: ECDH, X25519, 253 bits --- SSL handshake has read 3673 bytes and written 289 bytes --- New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256 Server public key is 2048 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE No ALPN negotiated SSL-Session: Protocol : TLSv1.2 Cipher : ECDHE-RSA-AES128-GCM-SHA256 Session-ID: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Session-ID-ctx: Master-Key: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX TLS session ticket lifetime hint: 7200 (seconds) TLS session ticket: 0000 - xx xx 60 d0 86 88 c0 26-2e 67 c0 e0 01 84 09 ab .,`....&.x...... 0010 - xx xx 95 f2 fa fa 1f f6-01 06 e3 99 23 2d 69 9a i...........#-x. 0020 - xx xx d1 f6 98 35 b5 f4-8f 91 47 b1 8e a6 d4 d2 *....6....G..... 0030 - xx xx b2 f4 61 f1 b0 7d-43 cb 66 62 c6 15 52 ad \*..x..}C.fb..R. 0040 - xx xx c3 f9 a9 f3 f8 e7-f2 7f b8 d3 0e 02 d2 da /...x........... 0050 - xx xx 0f 8f c1 1c 6e b3-f0 ae 4c ac 4e f6 8d 7c g.....x...L.N..| 0060 - xx xx 3b 2a 77 b3 c2 f0-2b e3 9f 73 1e db 07 6c /.;*x...+..s...l 0070 - xx xx a3 b5 42 74 de 4b-55 73 15 cf b0 97 c7 84 <...Bx.KUs...... 0080 - xx xx 65 ee cc 68 35 68-76 ef 7b 4a 7b 41 b3 94 ..e..x5hv.{J{A.. 0090 - xx xx 57 3f 74 a8 e8 0a-ec de 8b 77 49 f9 33 b0 `0W?x......wI.3. Start Time: 1643082971 Timeout : 7200 (sec) Verify return code: 0 (ok) Let’s investigate this response piece by piece. ...

“How do you store passwords in a database”? A very common question for back-end-oriented interviews. After conducting hundreds of technical interviews on different levels, I can confidently say around 50% of the candidates can’t answer this question. The most common answer I often got is “there is a package/gem/library we use, and it manages the password part”. Well, yes, frameworks, libraries, and packages cover most of the complexity nowadays, but I don’t accept this as an excuse for not being curious about essentials. Frameworks, packages, libraries, tools, text editors - they come and go all the time, but essentials just don’t. The ways we use to store passwords haven’t been changed much since I started programming, which was 15 years ago. ...

Cryptographic hash functions are complex mathematical calculations. Therefore understanding them requires a considerable amount of time and patience. However, they all have things in common: an input, a cryptographic algorithm, and an output. Recently, I had a chance to study some popular cryptographic hash functions, such as MD5 and SHA-1, and tried to understand how they really work. Wikipedia pages I linked include a considerable amount of information already, and more can be found online, but what I want to do was understand similarities between them and write my own primitive hashing function in Go. ...

Hybrid Encryption: Symmetric and Asymmetric Encryption Combined Both symmetric and asymmetric encryption has advantages and disadvantages. So, which one should we use? Well, nowadays we often use them together. Asymmetric encryption is often used to exchange private keys between parties securely. In other words, parties who would communicate establish an asymmetric encryption protocol in the beginning just to exchange private keys. When the private key exchange is completed, they keep communicating by using symmetric encryption - which is faster than asymmetric encryption. This is also how SSL/TLS works. ...

Symmetric Encryption (Private Key Cryptography) In symmetric encryption only a single key, in other words, a private key is used to encrypt and decrypt a message. Symmetric encryption is also known as “Private Key Cryptography” as the whole encryption is only based on a private key. Some popular symmetric encryption algorithms are: Algorithm Cipher Key Size Block/State Size Popularity Notes AES Block 128, 192, or 256 bits 128 bits 1 The best one. Still in use. Blowfish Block 32-448 bits 64 bits 2 Still quite safe, but slower than AES. Twofish Block 128, 192, or 256 bits 128 bits 3 Still quite safe, but slower than AES. DES Block 56 bits 64 bits 4 Not considered as safe anymore. 3DES Block 112, or 168 bits 64 bits 4 Not considered as safe anymore. RC4 Stream 40-2048 bits 2064 bits 4 Not considered as safe anymore. Pros of symmetric encryption: ...

The most recent versions (5.1 and 5.2) of Ruby on Rails has shipped with a new feature named as encrypted credentials which replaces the secrets.yml, and enables you to keep sensitive data in an encrypted file named as config/credentials.yml.enc. However, this feature only works with a single file that is config/credentials.yml.enc. Recently we needed to add some data in our repository, which we wanted to keep as encrypted, but that also didn’t really fit into the credentials.yml.enc conceptually. ...