Crypto & Encoding ​

UUID generation, Base64 encoding, and cryptographic hashing.

UUID ​

uuid/v4 ​

Generate a random UUID v4 string.

Signature: (uuid/v4) → string

sema
(uuid/v4)   ; => "550e8400-e29b-41d4-a716-446655440000" (varies)

Each call returns a new unique identifier:

sema
(equal? (uuid/v4) (uuid/v4))   ; => #f

Base64 Encoding ​

Functions for Base64 encoding and decoding of strings and binary data. Uses the standard Base64 alphabet (RFC 4648).

base64/encode ​

Encode a string to Base64.

Signature: (base64/encode string) → string

sema
(base64/encode "hello")   ; => "aGVsbG8="
(base64/encode "")        ; => ""

base64/decode ​

Decode a Base64 string back to a UTF-8 string. Errors if the decoded bytes are not valid UTF-8.

Signature: (base64/decode base64-string) → string

sema
(base64/decode "aGVsbG8=")   ; => "hello"

base64/encode-bytes ​

Encode a bytevector to Base64.

Signature: (base64/encode-bytes bytevector) → string

sema
(base64/encode-bytes #u8(104 101 108 108 111))   ; => "aGVsbG8="

base64/decode-bytes ​

Decode a Base64 string to a bytevector. Unlike base64/decode, this does not require valid UTF-8.

Signature: (base64/decode-bytes base64-string) → bytevector

sema
(base64/decode-bytes "aGVsbG8=")   ; => #u8(104 101 108 108 111)

Use cases ​

Data URIs:

sema
(string/append "data:image/png;base64," (base64/encode-bytes (file/read-bytes "icon.png")))

API authentication (Basic Auth):

sema
(define auth-header
  (string/append "Basic " (base64/encode (string/append username ":" password))))

Hashing ​

Cryptographic hash functions that return hex-encoded strings.

Security note

MD5 is cryptographically broken — do not use it for passwords, signatures, or any security-sensitive purpose. Use hash/sha256 or hash/hmac-sha256 instead. MD5 is still fine for checksums and non-security uses (cache keys, deduplication).

hash/sha256 ​

Compute the SHA-256 hash of a string. Returns a 64-character hex string.

Signature: (hash/sha256 string) → string

sema
(hash/sha256 "hello")
; => "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"

hash/md5 ​

Compute the MD5 hash of a string. Returns a 32-character hex string.

Signature: (hash/md5 string) → string

sema
(hash/md5 "hello")   ; => "5d41402abc4b2a76b9719d911017c592"

hash/hmac-sha256 ​

Compute an HMAC-SHA256 message authentication code. Returns a 64-character hex string.

Signature: (hash/hmac-sha256 key message) → string

sema
(hash/hmac-sha256 "secret-key" "message")
; => "hex-encoded-hmac..."

Webhook verification example:

sema
;; Verify a webhook signature from a provider
(define (verify-webhook payload secret signature)
  (equal? (hash/hmac-sha256 secret payload) signature))