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Echo crypto suite tag of the offer SDP in the answer SDP #17

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Merged
dennwc merged 1 commit into from
Aug 27, 2025
Merged

Echo crypto suite tag of the offer SDP in the answer SDP #17

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2 changes: 2 additions & 0 deletions sdp/offer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -539,6 +539,8 @@ func SelectCrypto(offer, answer []srtp.Profile, swap bool) (*srtp.Config, *srtp.
prof := &off
if swap {
prof = &ans
// Echo the cipher suite tag of the offer, in the answer
prof.Index = off.Index
}
return c, prof, nil
}
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50 changes: 50 additions & 0 deletions sdp/offer_test.go
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Expand Up @@ -473,3 +473,53 @@ a=rtcp-fb:* ccm tmmbr
},
v.CryptoProfiles)
}

// TestSelectCryptoSuiteTag ensures that when selecting a crypto suite from an offer/answer pair,
// the answer uses the same crypto suite tag as the offer, per RFC 4568 section 5.1.2 and 5.1.3.
func TestSelectCryptoSuiteTag(t *testing.T) {
answerProfiles := []srtp.Profile{
{Index: 1, Profile: "AES_CM_128_HMAC_SHA1_80"},
{Index: 2, Profile: "AES_CM_128_HMAC_SHA1_32"},
{Index: 3, Profile: "AES_256_CM_HMAC_SHA1_80"},
{Index: 4, Profile: "AES_256_CM_HMAC_SHA1_32"},
}

cases := []struct {
name string
offer []srtp.Profile
answer []srtp.Profile
exp *srtp.Profile
}{
{
name: "First",
offer: []srtp.Profile{
{Index: 1, Profile: "AES_CM_128_HMAC_SHA1_80"},
{Index: 2, Profile: "AES_CM_128_HMAC_SHA1_32"},
{Index: 3, Profile: "AES_256_CM_HMAC_SHA1_80"},
{Index: 4, Profile: "AES_256_CM_HMAC_SHA1_32"},
},
answer: answerProfiles,
exp: &srtp.Profile{Index: 1, Profile: "AES_CM_128_HMAC_SHA1_80"},
},
{
name: "Fifth",
offer: []srtp.Profile{
{Index: 1, Profile: "AEAD_AES_256_GCM"},
{Index: 2, Profile: "AEAD_AES_128_GCM"},
{Index: 3, Profile: "AES_256_CM_HMAC_SHA1_80"},
{Index: 4, Profile: "AES_256_CM_HMAC_SHA1_32"},
{Index: 5, Profile: "AES_CM_128_HMAC_SHA1_80"},
},
answer: answerProfiles,
exp: &srtp.Profile{Index: 5, Profile: "AES_CM_128_HMAC_SHA1_80"},
},
}

for _, c := range cases {
t.Run(c.name, func(t *testing.T) {
_, got, err := SelectCrypto(c.offer, c.answer, true)
require.NoError(t, err)
require.Equal(t, *c.exp, *got)
})
}
}
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