Simon Josefsson - Owner at Yubico

Simon Josefsson

Owner at Yubico

Stockholm County, Sweden

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Summary

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Senior

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Top School

Simon Josefsson is a seasoned security-focused software engineer and entrepreneur with 23 years of experience building and maintaining cryptographic and authentication software. As owner of SJD Ventures and an early leader at Yubico (former Head of R&D and long-term investor), he has helped shape real-world multi-factor and U2F tooling used broadly in the industry. His deep C and crypto expertise is visible in significant open-source contributions to projects like libssh2 and yubico-pam, where he implemented core cryptographic primitives and robust authentication flows. A longstanding Debian developer and Free Software Foundation member, he pairs pragmatic engineering with principled open-source stewardship. Based in Stockholm with an M.Sc. in mathematics and computer science, he blends hands-on systems programming with investor and board experience across security startups.

23 years of coding experience

M.Sc., Mathematics, computer science, M.Sc., Mathematics, computer science at Stockholms Universitet

English, Swedish

Stackoverflow

Stats

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0reached

0answers

0questions

Github Skills (17)

authentication10

user-authentication10

c1110

c1710

openssl10

cryptography10

aes10

encryption10

back-end-development9

lgpl9

lib9

clib8

c-library8

c-libraries8

autoconf8

Programming languages (21)

JavaC++CSSCSchemeRustMakefileM4

Github contributions (5)

Yubico/yubico-pam

Jan 2008 - Aug 2016

Yubico Pluggable Authentication Module (PAM)

Role in this project:

Back-end Developer

Contributions:161 commits, 1 push in 8 years 8 months

Contributions summary:Simon primarily contributed to the core functionality of the Yubico PAM module. Their work involved integrating the libyubikey-client for authentication, and implementing a user configuration file parsing to support multi-factor authentication. The user updated the module to support features like try_first_pass, use_first_pass, and LDAP-based authentication. Additional changes addressed memory management and deprecated features.

pamyubikeyauthenticationpluggable-authenticationyubico

libssh2/libssh2

Dec 2006 - Oct 2010

the SSH library

Role in this project:

Back-end Developer

Contributions:172 commits, 2 comments in 3 years 11 months

Contributions summary:Simon's primary contribution involved refactoring and enhancing the cryptographic components within the libssh2 library. They moved symmetric OpenSSL EVP crypto calls to `crypt.c`, implementing initialization, encryption, and decryption functionalities. These changes included adding support for various encryption algorithms such as AES, Blowfish, and CAST. Furthermore, the user updated the library to use generic APIs for hashing, HMAC, and RNG functions and incorporated support for AES-CTR ciphers.

ssh-librarysftpsshforwardinglibssh2

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