{"record":{"id":"b87e9da3209994d5","repo":"ory/hydra","slug":"secret-for-signing-hmac-sha512-256-is-expected-to","errorCode":null,"errorMessage":"secret for signing HMAC-SHA512/256 is expected to be 32 byte long, got %d byte","messagePattern":"secret for signing HMAC-SHA512/256 is expected to be 32 byte long, got (.+?) byte","errorType":"error_code","errorClass":null,"httpStatus":null,"severity":"critical","filePath":"fosite/token/hmac/hmacsha.go","lineNumber":57,"sourceCode":"\tminimumEntropy      = 32\n\tminimumSecretLength = 32\n)\n\nvar b64 = base64.URLEncoding.WithPadding(base64.NoPadding)\n\n// Generate generates a token and a matching signature or returns an error.\n// This method implements rfc6819 Section 5.1.4.2.2: Use High Entropy for Secrets.\nfunc (c *HMACStrategy) Generate(ctx context.Context) (string, string, error) {\n\tc.Lock()\n\tdefer c.Unlock()\n\n\tglobalSecret, err := c.Config.GetGlobalSecret(ctx)\n\tif err != nil {\n\t\treturn \"\", \"\", err\n\t}\n\n\tif len(globalSecret) < minimumSecretLength {\n\t\treturn \"\", \"\", errors.Errorf(\"secret for signing HMAC-SHA512/256 is expected to be 32 byte long, got %d byte\", len(globalSecret))\n\t}\n\n\tvar signingKey [32]byte\n\tcopy(signingKey[:], globalSecret)\n\n\tentropy := c.Config.GetTokenEntropy(ctx)\n\tif entropy < minimumEntropy {\n\t\tentropy = minimumEntropy\n\t}\n\n\t// When creating tokens not intended for usage by human users (e.g.,\n\t// client secrets or token handles), the authorization server should\n\t// include a reasonable level of entropy in order to mitigate the risk\n\t// of guessing attacks. The token value should be >=128 bits long and\n\t// constructed from a cryptographically strong random or pseudo-random\n\t// number sequence (see [RFC4086] for best current practice) generated\n\t// by the authorization server.\n\ttokenKey, err := RandomBytes(entropy)","sourceCodeStart":39,"sourceCodeEnd":75,"githubUrl":"https://github.com/ory/hydra/blob/4174065ffb052799890f7480f5360a877a67ffc1/fosite/token/hmac/hmacsha.go#L39-L75","documentation":"HMACStrategy.Generate refuses to sign tokens when the configured global secret is shorter than the 32-byte minimum required for HMAC-SHA512/256 (the signing key is a 32-byte array). This is a server configuration problem: the secret in the environment/config is too short (or empty).","triggerScenarios":"Generating any HMAC-based artifact (access token, refresh token, authorize code, device code) via GenerateAccessToken/GenerateRefreshToken/GenerateAuthorizeCode/GenerateDeviceCode when GetGlobalSecret(ctx) returns fewer than 32 bytes.","commonSituations":"Dev/test secrets like 'some-secret' left in production config; missing or empty OAUTH2_SHARED_SECRET / COOKIE_SECRET env var; docker-compose examples with short secrets not replaced during deployment.","solutions":["Set a global secret of at least 32 bytes (e.g. generate with: export OAUTH2_SHARED_SECRET=$(openssl rand -hex 32) or head -c 32 /dev/urandom | base64 depending on encoding)","Restart/redeploy the service so the new secret is loaded","Check for encoding pitfalls: if the value is hex/base64 encoded, decode before measuring or supply 32 raw bytes","Ensure all replicas share the same long secret, otherwise token validation will break next"],"exampleFix":"// before\nexport OAUTH2_SHARED_SECRET=\"supersecret\"\n// after\nexport OAUTH2_SHARED_SECRET=\"$(openssl rand -hex 32)\"  # 64 hex chars = 32 bytes","handlingStrategy":"validation","validationCode":"secret, _ := cfg.GetGlobalSecret(context.Background())\nif len(secret) < 32 {\n    log.Fatalf(\"global secret too short: %d bytes (need >= 32)\", len(secret))\n}","typeGuard":null,"tryCatchPattern":"_, err := tokens.GenerateAccessToken(ctx, req)\nif err != nil && strings.Contains(err.Error(), \"expected to be 32 byte long\") {\n    log.Fatalf(\"misconfigured global secret: %v\", err)\n}","preventionTips":["Generate secrets with openssl rand -hex 32 at deploy time, never hardcode short dev secrets","Add a startup assertion that the shared secret is >= 32 bytes","Keep the same secret (or a rotation list of >=32-byte secrets) across all replicas and generate/validate paths","Document the 32-byte requirement in your deployment checklist"],"tags":["oauth2","fosite","hmac","configuration","secret-length"],"backgroundTag":"hmac-secret-too-short","analyzedSha":"4174065ffb052799890f7480f5360a877a67ffc1","analyzedAt":"2026-09-03T14:52:41.581Z","contentChangedAt":"2026-09-03T14:52:41.581Z","schemaVersion":2},"datasetVersion":"2026-09-10T17:17:09.494Z"}